Lookin' awesome! As for materials to use for bases, I cut my bases and movement trays from Bass Wood. You can find whole racks of it from Hobby Lobby back in the crafts section. I recommend taking a single plastic base in your pocket with you and then comparing the depths of the base with the depth of the wood. Then it's simply cutting out the shape you want with a hobby knife. I also recommend buying a package of the square dowels that are the same depth as the sheet of wood that you get. You can use them to make borders for your movement trays. This is an image of what I'm talking about before painting it. You can customize these trays to work for skirmishers as well. Here is an example of a unit of Skinks that I completed and made a movement tray for a little while back. The wood is sturdy and doesn't warp due to being painted. Make sure you get Bass Wood instead of Balsa Wood. Balsa Wood is too soft. I hope that helps!