100% Polyester, also known as 'Dacron' can also be used. It has a tight weave and is very light. You can find it in fabric shops since it's commonly used in sewing as the inside lining for dresses. Stick it down around the perimeter and shrink it with a hot iron. It can then be stuck down to the rest of the frame with nitrate dope.
As for the fiberglassing, if it's done correctly, I'm convinced that it can be very nearly as light as any iron on film.