Yes, finding a way to heat a large piece is the challenge. I have heard that windshield makers place the plastic in a vat of boiling oil. But I don't know what kind of oil they use, and don't know how I would heat up a vat large enough to hold a piece the size I need. The skylight is about 35" square, so I need to heat up a piece a little larger than that. The flannel is a good idea. I will remember that, if I ever figure out a solution to the other obstacles.