massive reconfiguration time again.

Are you talkin about sanding epoxy primer? You don't do that. Epoxy primer is not sandable. It balls up and does not sand. Lay down epoxy primer and let it cure, then shoot a sandable primer over it. That's how it's done.
On another thread I have had a couple different ppl tell me that using SPI epoxy primer it can be sanded and top coated. Idk I have never used it.