hey that's too bad about your paint on the sub b-rat..
instead of sanding, why not throw your sub in a container with some Super Clean. it will strip off the paint waaay easier than sanding. if the paint is stubborn, put it in a container of dot 3, between them it will come out like virgin plastic again.
and if i don't use my airbrush, i always use Krylon. good paint, lays down smooth. good luck on the next paint job