I had the same problem with my tf corsair, I ended up resheeting it, but still had some waveyness but not as much. I ended up sanding the hell out of it to make it as smooth and properly contoured as possible. I am now getting ready to glass it. I have a lot of thin places in the wing now though. I hope it won't be a problem. The fiberglass should strenthen those areas I believe. I'd try to keep from adding filler at all, if possible, but thats me.

Ask caffeenman he seems to be very knowledgeable in this area.