That era (early 90s) HR usually used an aluminum two piece skin on the roof (seam down the middle) back by thin plywood with either wood or aluminum joist, foam board insulation between the joist and on the inside a piece of luan with foam glued to it covered with the vinyl. At least that how my 93 HR 1000 (aluminum joist) was and a friends 91 Imperial (had both aluminum and wood joist - wood at ACs).
That might give you an idea of how this one was assembled as well.
Ask if the owner has the owners manual. Mine included a brochure on the "structure" (walls, roof, etc).
On mine I had an area in the bedroom that had came unglued. Just like an older car headliner the foam beneath the vinyl had deteriorated. It was sagging in the middle of a 4 foot panel. We pulled it off, scraped off the foam, replaced with some foam from the fabric store and used spray adhesive to glue the foam to the wood and the vinyl to the foam. It wrinkled some but looked better than the sagging headliner.
Mike
Edited to add:
Mine had no water damage on the ceiling from leaks. Carefully look for signs of water leaks and damage. Water intrusion would be a deal breaker. Deteriorated foam headliner not as much.
Mike
