Thanks for the input. Travis, the elastomeric bumper is a regular steel one with about a quarter inch of black foam (urethane?) over it. A lot of the info I've looked at is all about patching tears on modern plastic bumpers, and since they are made from a bunch of different plastics, there are patching compounds that are designed for all of the particular kinds. PistolGripper posted a link from WeldGuru, and one of the products shown is a compound that can be sprayed on (with a spray gun) and it forms a flexible, smooth plastic skin over the bumper. This looks like something that would be useful for the last step--once you've gotten it to the right shape and filled the holes. I haven't read everything on the website but I don't think I've seen anything like bondo that can be used to level the surface. I'll keep investigating.