Open ALL the windows
, get a BIG fan to blow air through the trailer, get a charcoal type respirator/air mask, get some lacquer thinner and remove the glue from the smooth fiberglass surface. NO need to remove any fiberglass or gelcoat surface from the fiberglass.
No it's actually not that bad of a job to remove the contact cement/glue from the smooth fiberglass surface of the inside of the trailer from which you just removed the wall covering just "smelly" because of the lacquer thinner. A flat plastic "Bondo" spreader or similar item helps to scrape and remove the thinner softened glue without damaging the fiberglass surface. Wipe the fiberglass down AFTER removing the glue with your favorite smelling disinfectant, let the trailer continue to air out a day or 2 and you are done!
For all the old foam from your old wall covering that is still there after peeling off the wall covering I have found getting a big brick of foam or a big sponge and rubbing what's left of the old foam with these will quickly remove the old foam from headliners and your fiberglass wall leaving only the glue and some foam residue to deal with using the lacquer thinner and scrub process.