hey man, what you said is exactly the way to go. white on the inside, then your base color on the outside. as long as you are using a good plastic-bonding krylon spraypaint, you shouldn't have to rough up the outside. just take your time and do 2 or 3 coats. you dont have to get a solid base on the first go-around. just get enough to cover most of the mask, let it dry, and repeat. that way you prevent runs. (which are a b*tch!)
here's a 3 I recently started...
here's a 3 I recently started...