The halogen lamps are 50w, I've never tried white plastic, so will be interested in the result.
I do get the feeling however that the light will be a little harsh. Look forward to seeing the effect.
By using a white linen sheet draped loosely the light is diffused and scattered in all directions.
The ideal materials for creating a frame can be purchased here
http://www.screwfix.com/app/sfd/cat/...01311&ts=66376 this being 21.5mm overflow pipe approx cost £36
8 x 90 deg bends, 4 tees and 3 lengths of pipe. Then nick a white bed sheet when the boss is not looking.
Harry