One of the first and perhaps most important steps in rebuilding a travel trailer is to inspect and repair it's basic structural elements. This includes the frame on which the body of the trailer rests as well as the body of the trailer compartment. You need to inspect the metal frame of the travel trailer for rust. If the frame is damaged or structurally unsound, you will need to attend to that before moving on to the frame of the compartment.
Water infiltration is a concern, as it would be for any structure. Once water begins to infiltrate, it can compromise the frame by causing the metal to rust and the wood of the compartment's structure to rot. This lessens the travel trailer's structural integrity. In addition to repairing any leaks, you must replace any rotted wood in the travel trailer's structure.
Inspect the electrical system of the travel trailer as you are rebuilding it. Test all electrical connections inside the travel trailer as well as those that connect the travel trailer to the towing vehicle. As you are attending to leaks or replacing rotted wood, you will have easy access to the wiring inside the trailer. You might even need to replace all of the trailer's wiring.
While you are rebuilding the travel trailer, you should also examine its plumbing system, including toilet, shower and sink. Check pipes to make sure connections are sound. If necessary, replace old pipes with new PVC.
