I believe they have an aluminum frame rivetted together like Airstream and similar trailers.
Yours seems to have typical leakage problems. This can be fixed with seam sealer, new calking around vents, around windows etc.
Unless the body is damaged, or rivets worked loose. This will be noticable on close inspection.
Water damaged areas of the interior will need to be removed, cleaned, refinished and/or replaced. Don't forget, fibreglass insulation may be waterlogged and need to be replaced.
This can be a lot of work but not terribly expensive in terms of materials.
If the body is screwed together it is possible to take apart. It is actually easier to remove panels and fix damage from the outside, than from the inside.
Look on Youtube for videos by Mobiltec about repairing similar trailers. 1958
Deville would be most similar.