Will primer fix this?

I'm updating the lightning with a new paint job (metallic gunmetal) and some cosmestic upgrades. The most major upgrade is that I'm molding the rollpan directly into the tailgate, kinda like this: http://www.truckworld.com/Street-Scene/full-body-slam/full-body-slam4.jpg

Its just that I layed the epoxy on too thick at first, and after lots of handling of the body, the putty has cracks in it. Not big cracks, just tiny fractures that run short in several places. I've sanded everything down flush and now the cracks can still be seen, but when I run my finger along it, I can't feel any dips in the putty. Should I go along and flood it with several coats of primer, should I be ok? I'm gonna put putty in behind the rollpan too to re-enforce it so it doesn't shift and crack again.

That's a low truck, I would throw some primer on it, if the crackes are stll visible just add some putty.

I would say that the primer will not fill the cracks. Putty it again and get it perfect before spraying it