Assuming your sidewalls appear to be fiberglass (as opposed to metal), they are likely to be a thin fiberglass skin over laun plywood. The glass skin can be re-finished, even though it is thin and one must be careful about sanding. The same applies to the gel coat finish on a fiberglass boat, though. There`are Rv shops that specialize in re-painting and most boat repair shops can also handle it. But as Shayne says, it's quite expensive and a 91 Coachman is not likely to be worth it.
On the other hand, there are hand-applied paints for fiberglass you could try - most any marine store will have them. It's a lot of work and hard to get a nice smooth finish, though. All the decent ones are atwo-part epoxy finish, but I have recently seen some "one part, no mixing" fiberglass finishes advertised. Don't know how well they work, but they are rated for direct application to fiberglass surfaces.
Here's a couple contenders...
http://store.nationalpaintsupply.net/meglgositofi1.html
http://store.nationalpaintsupply.net/blwapoto.html