When I have used the bed-liner stuff on cage work I would make sure to wipe it down with a good degrease. I have had good success with the Rustolium bed liner.. Never primed it just a good wipe down maybe a scuff with a Scotch Brite pad..
Also the bumpers come with a fresh sanding from the DA so other then a couple of spots it should stick pretty good.. Things that I have seen mess with paint.. Oil, cold day, wet day, bad batch of paint..