Here is what I have come up with.
My Swagmen bottom tire holding bike rack weighs 109# with 2 adult bikes on it. Looks like this. The main bike rack is Swagmen but I made the stand it mounts too. They call them platform racks. Mine had a 2” straight tube shank. The ones on line I searched tonight seems to have a smaller size and an adapter. Don’t know if they all do or not. Maybe something new. For this setup, the 2" straight is a better option if you can get it.
Here is one place you can buy them
Amazon.com: Swagman XC Cross-Country 2-Bike Hitch Mount Rack (2-Inch Receiver): Sports & Outdoors
I also estimated that the center of the bikes weight was 12” behind the rear bumper or 274” from the tow ball and 76” behind the rear axle on the TT.
Using 109# of bike and rack at the dimensions you gave me and adding the 12” over hang comes out to:
109# bike and rack
Adds 151# weight to the TT rear axle
Removes 42# weight off of the tongue weight.
Now let’s look at how Sunline made this unit. A 2006 T2075 is listed as having a dry weight of 3,910# with a dray tongue of 570# on a 5,500# GVWR TT. Sunline did a good job in the weight and balance area.
That 570# dry tongue on a 3,910# dry TT is 14.6% dry tongue weight which makes a good stable towing TT empty.
Now not putting any gear in the camper yet, Lets add 109# of bikes and rack up’ing the GVW to 3,910# + 109# = 4,019# On that GVW you will loose 42# of tongue dropping the 570# - 42# = 528# or 13.1% tongue weight. Which is still OK. Basically you will loose 1.5% tongue weight from where ever you are today with the bikes on the back.
Looking at the floor plan there is storage under the bed, side and top cabinets in the front bed room and a pass thru cargo hole. That front storage adds tongue weight.
The kitchen is over the axles to the fridge being maybe slightly behind the rear axle.
The rear ward in the bath room allows storage to offset the tongue weight.
By the floor plan, not talking about the fresh water tank, loading the camper the tongue weight is going up and could be by 250 maybe 350#. How much depends on what is up front and what you have in the rear ward cabinet.
Don’t know if you haul fresh water to camp. That 32 gallon fresh tank is ~ 266# by itself. If you do haul fresh water, what is the dimension of the tank center to the tow ball? We can add that to the mix to see if there are any issues or not.
Now to the 2” bike receiver. Your right, the Sunline bumper is not going to take much of anything. Even the spare tire can cause havoc and should be over next to the frame support.
Hanging bikes 76” behind the rear axle creates a fair amount of bounce on every bump the TT goes over. If you are going to go to a rear mount, it really has to be solid.
By using the 3” tube with the angles welded to it and to the frame it creates sort of a torque tube. Then the 2” pin box on the torque tube. This creates a flexing situation again 76” behind the rear axle.
If you want to go the 3” tube route I suggest the 2” pin box be about 2 to 2 Ĺ feet long inward to the TT. Then do another cross member to tie the end of the 2” tube from twisting the 3” bumper your going to make.
OR leave the Sunline bumper and go to the frame with a heavy support at the end and then again 2 1/2' feet inward again to stop that heavy twisting action.
EMAM here on the forum had a custom receiver hitch made on the back of his T2499. He has pics on here somewhere showing what I can describing. Poppy and Nana’s looks similar as I have seen theirs.
If you have not bought your bike rack yet, I recommend going for the type like I showed that holds the bikes by the tires verses the type that hangs by the center bar of the bike frame way up high. Those top type carriers create about a 5 to 6 foot lever twisting into the receiver. The bottom racks that hold by the tires do not have that same leverage.
I would also recommend before doing the bike rack, get the camper weighed and a known tongue weight. Then you know what your tongue weight % is in relation to the loaded GVW. The bikes on the back will lower that by approx 1.5% and the added frame will reduce it a little more too.
I do not see the heavy heads up with your floor plan like some others are but the bikes do take a bouncing back there. Cable them to the frame some how in case they let loose, at least you are dragging them.
You will be the one who has to make the final decision. I had them back there once. Did not have the heavy frame under the camper but I learned what not to do.
Hope this helps and good luck
I’ll see if I can find that EMAM bike rack pic.