I've been using SEM Dual-Mix products and have been pleased with the results. On my current build I've used their weld bond adhesive to install a new rocker panel, patch panel adhesive for some small stuff, self leveling seam sealer and regular seam sealer on welded seams and to replace some of the old dug out sealer prior to painting.
Most metal bonding products require both surfaces to be good clean bare metal, and roughed up with a 36 grit disc for good bite.
The seam sealers I use can be applied over bare metal, oem finish, or epoxy and urethane primers, and are paintable right away.
Here is some of the seam sealer I applied last fall during my paint prep.