JB Weld did not hold up. I ended up drilling, deburring, self etch primering, painting, and sealing holes for the factory cleats to hold the subwoofer, and then bolting the brackets in place through said holes, and then covering with flexible seam sealer afterwards. Just to follow up on what works and what doesn't. The cheaper way would be Keith's butterfly bolts. Epoxy alone will likely not be enough.