Thanks man. Think I understand better now. Definitely need something with body to fill in the gaps, especially the corners. All looks pretty good under there. Not even a hint of any rust, thankfully.
Doing the Internet thing, it seems like the urethane doesn't stick the rubber to painted sheetmetal very well. At least a couple guys had issues there. Will head to Napa tomorrow for the 4203.
Appreciate the help!