What can I use to bond 2 parts of my car body together, if they're cracked?

I have a 98 oldsmobile cutl, and some of the molding down in the wheel well is cracked, and is coming apart from the body (like, where the permanent mudflap is). As a result of this, the entire bumper is becoming looser and looser. I know that I can fill the crack with something, and easily clamp it together so it will hold, but I'm not sure on the material to use. Epoxy? Bondo? I'm not sure how deep it goes, so something that foams or has a lot of substance would probably be better. Thank you for the ideas.