Too bad you could not have spent the bucks for an epoxy primer on the outside. My question is why do you have so much rusty pitting left after blasting?
As far as the backs of those panels are concerned ZR away. Seal up those surfaces. Understand the Zero Rust would have worked better without the junk primer between it and the steel.
On the outside question, If you were going to put ZR over everything first, the proper approach would be to leave that film alone and build your sandable system over that. This is done for 2 reasons. #1 ZR desn't sand for sour owl feathers and #2 you want to leave the ZR film intact to provide the seal. Earl scheib is not going to stand behind any issues concerning compatability between what ever is on the rig when you bring it in and what they will apply. If anything lifts, the warranty is written on the head of this pin and they wrote really big......
