Gm Primer - Sandblast or scuff before epoxy primer?

T

Turbotoys

I am doing collision repair on a 2015 traverse and I have inner and outer frame rails new from GM in their black primer (I am assuming an epoxy of some sort) should I sandblast all the GM primer off and primer with SPI Epoxy or should I be fine just scuffing with red scotchbrite and priming with 3 coats SPI epoxy before plug welding them together?
 
Sand it and epoxy the ecoat, factory parts are a true ecoat so no need to take off.
 
Thanks for the replies. One other question - is a red schotchbrite enough or should I sand it with 180 ? it has a lot of different curves and crevices to roughen up.

Thanks again for the replies!
 
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