O.K., I've been all over town (Home Depot, Lowes, OSH, and independent stores) and can only locate the white foamboard insulation made of the ice chest type pressed together foam balls. It finally occurred to me to call the hobby shop and ask since they specialize in model railroading. The owner has indeed used the better foam material (the pink or blue stuff) for a layout base but explained it's not available here. I'd have to travel long distance to another city to buy it. Since I'd rather use material I can get locally, I need to go to plan B.
Plan B would be to use the white board but for extra support, I'd first attach a 1/4" (or thinner if I could find it) piece of plywood to the frame, then glue about a 1" thick piece of the foam solid to that, and of course have wood side boards come up even to protect the sides of the foam. And I would use extra foam board to do hills or whatever. I'd either use a hot wire or file to carve features, which might be messy but I'll just keep the vacuum at hand.
I'm thinking this could work, especially after looking at a finished craft project at Michael's the other day: I don't know if it's popular everywhere but here in the southwest some schools do these kits of old Missions which consists of the same type of foam board in pre-cut sections that are glued together on a base, then painted and detailed. The model on display has been used for a few years (and handled by many a curious person) and has held together well. An employee explained that "tacky glue" is used for the foam (a type of white glue but is designed for a wider variety of materials). I also asked about a rough stucco like material on the outer walls, and this turned out to be plaster of paris (which I didn't know would stick to foam but seems to bond quite well and can be textured). I liked that idea because not only could I fill any separations in foam sections but I'm pretty sure I could press actual rocks along half dry material coated over parts of the foam board and create exposed "rock" sections in the hillsides or even just mold it with tools. And it's compatible with glue and paint so no problem there.
My question is; is there any serious flaws anyone can see in this plan or anything I should watch out for with these materials? I already know about the fumes from a hot wire going through foam so would do that outside with a fan, but is there any thing else? I think I recall someone else mentioned they had used the white foam but don't know if they had any unusual experiences with it during construction or over time.
Any advice?
~Brad H.