A group 24 Deep Cycle RV/Marine battery is probably best bet for the 15. It will run longer than a car battery and drain deeper before it craps out completely. Also your trailer brakes "Breakaway" or "Deadman" switch is connected to the battery. In case your trailer separates from the car/truck, there is a cable that attaches to the car, pulling out a pin in the "Deadman switch" turning the brakes FULL ON.
If your vehicle has a Factory 7way plug it may have the 12V already wired but NOT CONNECTED to the Fuse panel under the hood. The wire will need to be dug out of the wiring harness and connected to the properly fused B+ Post at the Fusing panel. It's usually switched (IGN ON) so unless your engine stalls or the alternator craps out, it will charge the battery while driving. Same thing with the trailer brake wiring (unless both are already hooked up and working already).
If you don't plan on using the Furnace by all means put some screen (metal only) material over the outlet and inlets. But make sure it's clear and clean 1st. Bugs, hornets, etc., may not appreciate being locked in what is literally an oven. Blow some compressed air into the inlet and let it blow for 30 seconds or so (use a blow gun with a short extension should you p.o. some hornets, wasps, etc.). Then fire it up and make sure it cycles a few times to burn off carcasses, etc. Then blow it out after it cools. Cover inlet and outlet with screens.
Water tank fill and Shoreline water inlet both use the same lines internally but the two sources are separated by one-way valves at the Waterpump.
The Water Heater is most likely a 6 gallon unit and operates basically the way an older home gas water works. Turn on Gas bottle. Then on the regulator turn the off/Pilot/On knob to PILOT, and push the RED Button next to it. Light the pilot with a extension wand lighter (BBQ Lighter). Keep red button down for about 30-45 seconds or until pilot light stays lit when you slowly release button. Then turn Off/Pilot/On knob to ON. The burner valve will open and depending if an Atwood or Suburban you'll hear a slight whoosh(Atwood) or a loud Thump Whoosh (suburban). This is Normal. It will then automatically keep water hot. Just don't expect to take long HOLLYWOOD Showers. The shorter and less water the better (don't mess with Momma. When she wants hot water she wants it yesterday for a shower, not next week.) Best to take a sink bath in cold water and leave her the hot.
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