Dioramas

If you get a chance, also pick up some Cell u Clay from a nearby arts and crafts store (i.e Michael's). It is perfect to simulate groundwork, and is easy to use and can also be colored using acrylic paint. Another suggestion for material is cat litter. Cat litter is great for rocks and small debris. I base alot of my Diorama groundwork on Verlinden Productions great books. It took some time to get used to the material, but once you get the hang of it, you'll love it. So if you can, pick up a few of them.

If your going to do a large hill build up with foam the use cell u clay or plaster of paris for final contuors to save weight and don't overlook model RR scenery as an option for scenery etc.

I was planning on using some of the RR accesories as trees and underbrush ect. What I have so far is some hard styrophome with one side cut into a gradual slope. I was planning on sanding it dow and giving it contors and a slight bumpy texture to the ground. Then use RR green gravel like material for grass and underbrush. Question though what type of glue should I use to glue the styro together and to the plywood base I'm going to use? Thanks for the help and please give any more suggestions.
The Bigguy

Bigguy, have a look at this site.

http://www.digitaldioramas.com/

There are a few step by step diorama articles and the forum makes for good reading

PVA glue (wood glue) would work great with Styrofoam and any wooden bits. If you use plaster of Paris or similar thing, add a good dose of PVA glue to your mix, it will make your dried plaster that much restistant to chocks... Anybits that stick out of your diorama should really be ready at the time you add the fresh plaster to your base, so that they can easily be included. Failing that, you might end up with odd-looking stuff. Use PVA glue to secure those bits into the fresh plaster. Oh, also, to ease the painting of your soil, add some acrylic or water based brown paint to the mix too. I use artist kind of paints in tubes rather than 'normal' modeling acrylics (WAY cheaper!). You should find that stuff in any art/craft store.