If you're going to put a massive chunk of heavy plastic in your wing, make sure it's fiber reinforced bondo. Regular bondo is very weak and prone to cracking, no body fillers are really meant to be applied that thick.
What is the wing made of by the way, urethane or fiberglass? If it's fiberglass, you're fine, but if it's urethane you'll have all kinds of problems because the urethane is a lot more flexible than the bondo. The paint will crack along the edges, etc.