Srt-68 Barracuda

I use etch primer because that's what it does. It etches the steel so that it will hold onto whatever you put over it. It's expensive.

Urethane (poly) primer will come next, after initial blocking. 2 wet coats of that. It's not cheap either. You can spend a hell of a lot less on primer, and that's what most body shops use on their production jobs. Who cares if it's junk if it's good enough for Geico.

Sparing expense on primer is one of the dumbest thing you can do at this point.