I too, would steer away from Bondo. It's acetone / toluenne based, and that might eat the wood. Also, it's a filler, not a bonding agent.

Epoxy & microballons for bonding / filler, or a 'Fill-n-Finish' wood grain sealer.. (But don't expect it to hold onto / bond with anything. it's just a filler.)

Epoxy & Microballoons sounds like what you want. Be sure to remove any 'gelcoat' and any paint. Scuff it up well for good adhesion.

Dunno what you mean by 'Wheel pant pockets' though..