shiny white plastic would work really well so long as the surface is fairly even. I've used seratone which is a white shower/bathroom lining product sold here in NZ which is really quiet shiny, even, flat, waterproof (my humidity level is about 59/60%RH) and as it's a composite wood product I can cut it, glue it, screw it etc - the draw back is it is F**King expensive but I had some left over from doing my shower If you can mount your plastic evenly and with as little interruptions (ie screws through etc) as possible then I say go for it - especially as you'd probably get it at staff rates or something