Initially I was going to just leave the crack on the outside and only do my repairs on the inside, but I figured I might as well try it out on this area that's not visible when they bags are installed on the bike, it's... Okay. I've read about adhesion promoting primers that can work with polypropylene that will actually allow bondo to properly stick to the surface, so I may try that out if i need to make the top side a little ugly.