Polystyrene is something I havent worked with much, I have worked with a material for Marine applications called Centra, its expanded PVC sheets and is pretty brittle but easy to work with, bad thing is the price, $75 a sheet for 1/4" 100 for 3/8 and 150 for 1/2. Its also a pain to paint because you need to prep it by sanding the entire surface then prime it with expensive primer. Thank everyone for their acknowledgement of my service it was my pleasure and I loved it almost as much as I love my Country.
I'm trying to start getting the ratios right for the dimensions.
Reading your post, a sandcrawler would have worked too