If you are going to use a bike inner tube get a HD (thorn proof)one. They come in different weights. I would just cut the tube and slide the hinge inside the tube and put my screws with washers through the tube/hinge/tube and into the wood. Double seal inside and out. Probably even better if you used T nuts in the camper and bolted the hinge on. That way you could replace the tube annually. Tubes do get beat up by UV.
KISS Principle = Keep It Simple Stupid.
Your best defense against Murphy's law!