I've got a pretty nice Whirlwind except for the head. It looks like it was in the elements for a while, and the wood on one side has started to delaminates.
I think trying if I tried bondo over this, I would be asking for trouble. My only other idea would be to use a skill saw to make shallow cuts just below the damaged area, sand it down, and patch in a thin piece of ply wood. Then cover the joints with bondo.
Any other suggestions?