Let's take a minute and break down plasti dip and spray paint, and how they react with foam.
Plasti dip and spray paint are both powered by aerosol. Certain types of foam (styrofoam) are broken down and react with aerosol sprays. Other types of foam, such as eva and craft foam, do not get broken down by aerosol. Therefore you can spray paint right onto them.
Plasti dip is great for filling tiny bubbles that are present on foam, and makes for a good surface for the paint to adhere to (I specifically use krylon fusion, as it is designed to adhere to plastic/rubbery surfaces).