Here's a link to a FAQ on aircraft fabric coverings:
http://www.sacskyranch.com/polyfiber.htm They say 20-30 years lifetime.
Just a thought: suppose you took your Geo Metro, CRX, or whatever you're ecomodding, and went over the bodywork with a hole cutter, so as to give you just a mesh framework, then covered that with doped fabric? (Of course making any aerodynamic shape mods.) How much weight might you drop?