I have had four good Sunline friends have leaking water heaters in the past few years make a big mess in their camper. The forum also has several members reporting water heater leaks and damage. Fitting leaks or pinholes in the tank seem to be the main modes of leaks. The worse part, the leak can go undetected and create large amounts of water damage to the camper even when the owners are camping in it, not realizing there is an issue.
The last friend had heavy floor rot under the water heater requiring some major floor repairs on top of a new water heater.
Most Sunlines in use today have older water heaters, including ours. Ideally, some system or method is in place to help prevent floor damage and alert when a leaking water heater starts. If you can address the leak as soon as it starts, the recovery is a lot simpler and cheaper.
I have come up with two methods to try and help the cause. The first method, a drain pan under the heater, is a more involved upgrade and fits when you add a new water heater or have the water heater out for some reason. The second method, a water alarm, is simple, and almost anyone can install it. Both can be used together or separate.
Method 1. Add a drip pan under the water heater. This will address the common known fitting leaks and tank pinhole leaks. One of my friends with a leaking heater did a pan of sorts under his heater, which sparked the idea for me. There are many ways to do this, and here is how I created a drain pan.
I installed this drip pan in my 2004 T1950 project camper. I had the water heater out for major camper restoration work, and before re-installing it, I created the drip pan and a drain.
I started with a 0.030" thick 6061 aluminum sheet. I have a 4 x 8 ft. sheet, and some scraps left over from a long time ago project, so I used it. Home Depot/Lowes sells thinner sheets (about half as thick) in, 24" x 24" or 36 x 36" and they will work too. The HD/Lowes prices range between approx. $25 to $35 plus tax.
I will do this in pics so you can see how I did it.
Start with a sheet large enough for your space in both length and width. I created a 3/4" high lip up on the three sides of the pan with a 1/2" lip on the front, which will fold down over the camper siding. You need to measure the opening in the camper with the heater out for the width. For the length, the pan needs to extend beyond the back of the heater and under your pipe fittings. The goal is the pan fits in the camper opening left to right with the sides bent up and is long enough to catch fitting drips.
Start by marking off the pan width and length, including the bent sides in the flat position. Cut the sheet to that size. Mark the right side and rear side to create a 3/4" bend up. The front needs a 1/2" bend down marked off to create a sealed lip at the bottom of the camper siding.
Next is bending the sheet into a pan. Start with a 3/4" x 3/4” corner notch at the rear of the pan and a 1/2" x 3/4” corner notch at the front.
Since my sheet is thicker, I created a poor man's bend brake with two pieces of leftover angle iron and C clamps. I want to bend the right 3/4" side up first. Position the corner cutouts to be right at the angle iron edge.
I used a separate piece of angle to start the full bend, and this is just enough to create a creased edge—about a 30-degree bend. Tap the loose angle iron with a dead blow hammer.
Finish the full 90-degree bend with the dead blow hammer against the lower clamped angle iron.
Next, mark off and bend the left side 3/4" up. Here, you need to mark off the "right" width to fit the opening in the camper. Check twice, bend once.
Mark off the dimension you want to bend at from the first side bend. By measuring from the first bend, you compensate for any bend error on the first bend. I used two combination square heads on a scale as an inside caliper to measure and mark the next bend line. You can use a tape measure if that is all you have. Just be picky. If this is too wide, the pan will not fit in the hole. The pan can be a little narrower, but not a lot.
Notch the two corners like the first time.
Bend the left side up like you did the first time. Align the bend line accurate to the angle iron to create a bend parallel to the first bend. The pan will look like this with 2, 3/4" sides bent up.
Test fit the pan in the opening to make sure it fits the way you want it to. If it does not fit, correct it now before going any further. It fits, yeh!
Next, bend the 1/2" front lip down. Load the angle iron brake like this. Slowly start bend by hand, finish with dead blow hammer.
It looks like this when done.
The last bend I had to do with metal bending pliers. If you do not have the angle iron setup, you can do all your bending with these; the angle iron only makes it easier to create a straight hard crease.
Start crease with about a 30 degree bend across the sheet with the handle bender.
Complete the bend.
Test fit the heater in the pan out on the bench.
The front bend lip
You may notice the heater tank is not in the center with the front mounting flange. Also, the water tank is not square to the mounting flange from Atwood. You may never notice this until you put the heater into a square pan.
Test fit the pan and heater in the camper for fit and where the drain tube is to go. Mark the drain pan area where to drill the drain tube hole.
I ended up using a 3/8" home toilet supply tube as the drain tube. It has a flange on top, is made of copper, and it only costs $3.50.
https://www.menards.com/main/bath/to...roduct=6640587
The supply tube that looks like this. Measure and cut to length. The tube will stick out under the camper 3 to 4".
After marking the pan, remove the water heater and C clamp the pan in place so it will not move location when you are drilling the drain hole. Drill the pan drain tube hole and the floor. Try and not drill too deep, or it will wrap up in the floor insulation. Use a screw driver through the hole to create a hole in the insulation and mark the bottom black membrane where to cut a small hole for the tube to come through. Using butyl sealing tape, create a water seal under the drain tube flange. Use two stainless screws (#8 x 1") with stainless flat washers and screw the flange to the floor. You also need to use butyl tape in the area of the screws.
Under the camper, I put plastic window screen on the end of the tube to keep mud daubers and other insects out of the drain tube. The 1/2" ID water hose was split and trimmed to compress around the 3/8" OD tube. It makes the small worm gear clamps work better.
Caulking still needs to be done on the back two corners of the pan to seal them and to seal the drain tube to the black membrane. Install the water heater as usual.
The drain pan looks like this when completed inside less the corner caulking, the hot water line, and the 120 VAC cable to the electric element.
The drain pan will collect and drain off any water that lands in it. Since we just rebuilt the entire floor system under this heater and using a 16-year water heater, the pan was the right choice. We will also add method 2.
Method 2. Add a water alarm on the floor of the water heater. This method is not new, houses use it often, just a different application, and can be installed in almost any camper with little effort.
I am going to use this rope style alarm, $35 plus tax.. Honeywell Home RWD42/A Honeywell Defense Water Leak Alarm with Sensing Cable, RWD42
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
You place the rope at the floor level around the water heater. It comes with a 5ft rope sensor, and you can add extra length if wanted. The alarm box is battery operated. When moisture is detected along with the rope sensor, the alarm will sound. The system will not stop alarming until you unplug the sensor or the water dries up on the rope.
Honeywell used to have an older model I liked better, but they discontinued that model.
I bought the one linked above. The system does work; it just looks cheaper than the older one I have in the basement. I have not found a comparable model with the alarm and sensor at that price or close to it. High-end rope alarms which cost over $100, open up a lot more options. They just cost a lot more and some need 120 VAC. Battery operated water alarm systems for sump pumps, or anywhere water spills that are made with two metal sensor pins to detect puddles are also options; those style alarms just do not have the rope feature for a larger detection area.
I will add one of these water alarms to our big T310SR as it also has a 16-year-old water heater. I will post pics of them when I get them installed.
Hope this helps
John
For more pics of this project, see my Flickr page here
https://www.flickr.com/photos/camper...57718076754068
The rope one in that case, would of just told you sooner. 
well no. I just recalled the saga you had with your soggy wet issue from a water heater fitting crack while you were camping. You were fortunate, you found the problem the day it happened (or the night it happened) if I recall right. You took action ASAP to dry out the basement of the camper and inside before damaged wood came. I'm sure you recall the pain of that cleanup. 
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