Do you have some tips for working with the craft foam? I've only used it as base areas for area terrain. It never seems the easiest thing to cut precisely?
Well, I usually stick it to some cardboard before I start cutting it. The craft foam isn't very firm, and can also tear if you don't use a sharp blade. I make cuts on the foam side and cut through to the underlying cardboard. I find if I cut the cardboard side up, then it tends to tear.
This can make it awkward if you need to draw guidelines for features and don't want to mark up and score the foam... To avoid that, you can cut out your forms first, then attach the foam sheet and cut off all the excess (like tracing an outline).
For texture, a dull pencil point makes for a great etching tool and I use the end of a bent paperclip to make rivets or nail holes... For the wooden grain effect, I just freehand cut a series of messy slices in each plank with an xacto. Looks great if you ink it with some brown...
I prime all my terrain using black gesso--and I think that adds a bit of firmness to the craft foam and protects the texture...
Like most things, I think it's just trial and error--but I've found it very useful and much easier to carve than insulating foam, foam core, wood etching or plasticard...