painting foam rubber

I've been asked to paint the backdrops for a school production, and they're made of sheets of foam rubber. There's about 24sqm to cover in a base coat of white, some black windows over that (less than 1/2 the 24sqm) and then a "green hue" over the whole lot (think Emerald City from Wiz of Oz and you've got the idea).
I think water based acrylic will soak into this stuff, so I was leaning towards sealing the foam first with a water-based sealer of some kind; spraying several very light coats to build up a base.
Any ideas on sealer type, whether regular house acrylic for the white and black would work over that, and if I can get a translucent emerald green to go over the top?
Any help much appreciated thanks.
Oh, and I have a week to get it done!!!