E-Coat on new fenders

Hey guys, I have 2 new AMD fenders, they are e-coated from AMD... I would like to spray the fenders in epoxy primer. What is the process to prep the fenders? how much of the e-coat do i have to remove?
I have heard that i can just "scuff" the e-coat with a red scotchbrite and ive heard that i should sand it all off... any suggestions from real experience would be helpful, thanks in advance..Rich
Some manufacturer's e-coat is good, but some are garbage. AMD has always been good. Body shop rule of thumb is to rub a spot with acetone on a rag. If none comes off on the rag, it should be left on, then scuff, clean, prime.