ideas for terrain:
Table covering- Plain sheets can work, especially if they are a neutral color: brown, green, grey, etc.
Sandpaper- Some foam you can sand to get a smooth finish.
Safety- Always be extra careful when cutting foam or really anything. CUT AWAY FROM YOURSELF.
Glue- Use the right glue for the job. Don't use superglue on foam...it eats it. Use white elmers glue or wood glue for foam. Glue can be watered down or used straight. If it oozes out from under the foam...cover it up with sand or maybe kitty litter (ballast)...or just wipe away the excess. White glue dries clear translucent.
Supplies- Almost anything can be terrain. The guts of machines and radios. Old containers and plant pots. Lids. Pretty much anything. Soon you'll drive around and see stuff and say "hmmm, that would make cool terrain!"
Paint- The propellant of spray paint eats foam. Make sure you prime foam with brush-on paint first to seal it.