Don't do it!! Putting your UHMW into the Powder Coasting oven might work to make it stick to your metal surface but at the very minimum it will not be UHMW when it cools down. The bond will fail quickly. Heating to above 200 degrees F changes the molecular structure and it will not wear like UHMW does afterwards.
Some special adhesives will work to some degree, but I strongly suggest mechanical fasteners. Weld studs to your boat and countersink the UHW or drill and bolt, then seal the holes. :idea: Check into weld washers for one good method or capped elevator bolts.
