Our 16ft U-haul
came with a hammock that kinda 'plugs in' over the front dinette and stores in the privacy room of the trailer. U-Hauls are double walled. The hammock states it can hold up to 150lbs. It's made of a heavy netting of sorts. It must be strong as ours is original from 1985 and spent 10 years in the U-haul
rental program. I can email you some photos if you send me a PM with your email address attached. I don't know if you can duplicate it exactly since mine is factory made, but it'll give you an idea of what the hammock idea is.
This past summer I took my niece and 2 nephews (12,11,10) camping for a long weekend in Michigan and we were quite comfortable. Could have possibly taken 1 more on a mattress on the floor even!