A few years ago a guy who used to post here built a profile Depron 3D plane for .049 power. His screen name is Dickeybird. The plane came in under 10 ozs if I remember correctly. Anyway he claimed that the Depron was fuel proof enough for this plane's purpose. I built a similar plane and made sure that I wiped it down good after every flight. The plane didn't last me long enough to really test it's long term ability to resist fuel damage, but I think Depron makes sense if you figure your 1/2A 3D model is just one "tail touch" from being sent to the landfill.
since then I've built similar models using nothing but 1/4 x 1/4 hard balsa sticks for the most part. Cover with craft store cellophane and 3M77 adhesive for a fast and light way to go.