When you say white foam, do you mean the foam with the little beads in it? How does it hold up. I worry all the time about a little bump knocking loose something.
You are quite right about buying the paint store mistakes. I found a florescent green primer that I just love for painting the bases of all my pieces. It gives them a signature color and pulls all my pieces together. Also, much of my paint comes from a company that recycles old paint. I went one time and filled up two large boxes full of paints, for free. Some of the paint was dried up of had other issues. I just got rid of them. The good stuff is still being used. Some of the stuff had to be repackaged, so I used old plastic bottles I get Miracle Whip or Planters nuts in. And I never get enamel paints.