I dont think you can in the corners case, i think the plastic is easily ruined by the oven heating project. Not sure about this but i think i recall reading a post about it a month back or so.
no, fiberglassing is a messy process =P, come take a look at my hands, even with latex gloves on i manage to be covered in the crap, and fiberglass doesnt wash off, more like it wears off.