Thanks for the responses. Will take a trip down to the generic arts store in town at some point with a list of things to look out for.
Not to pick favourites, but cork was a good idea for less messy, and I think they might have some sculpting blocks of the stuff, or similar, in the store.
Next task: best foliage suppliers? The theme is sandy (as my army bases are) but there will be heavy use of dead grass and desert-like shrubbery, maybe even some trees, just like you'd expect rocky near-desert lands to be. Plain desert is boring and why I want to start a new one in the first place. so looking for some good examples. Please and thank you.