Same here with a Palimino. I have mostly fixed the back of it but its still a dry weather only camper.
I tore off the old rear then cut 1" off of the back of the floor and when I made a new rear wall I then made it go an inch lower then the floor so it would sit on the truck bed/tailgate rather then sit on top f the floor which sits on an inch above the bed on 4 thin steel channels. I also widened the bottom to about 5' instead of 4' to give more support to prevent it from opening up. The door still popped open so I bought a normal household deadbolt and hacked it up to fit the thinner door and made it mostly work.
I tore off the old rear then cut 1" off of the back of the floor and when I made a new rear wall I then made it go an inch lower then the floor so it would sit on the truck bed/tailgate rather then sit on top f the floor which sits on an inch above the bed on 4 thin steel channels. I also widened the bottom to about 5' instead of 4' to give more support to prevent it from opening up. The door still popped open so I bought a normal household deadbolt and hacked it up to fit the thinner door and made it mostly work.