So, I've decided to go with mdf for a base, its particle board like plywood only not warped. Anywho, Now I'm thinking about how to have a river, mountains, grade changes, and rolling terrain to look realistic. My two approach thoughts are: 1. Use foam as a base and carve out the scenery (dips, canyons and such) and add foam for hills and mountains, if I go this route, I need suggestions on stores online or local where to pick up foam. Home Depot and by association Lowes are eh as they sell foam, but the layers are kinda on the thin side, at least for HO. 2. Build the rail all on balsa wood. By this, I mean even for the "ground level rail" it would be built upward from the base in an elevated fashion on balsa wood, kinda module style and then I'd have to use some type of covering that would allow for the adding of trees, grass, small structures, I'm not sure what modelers use here. 3. Some other plan I'm not thinking of.