I don’t think it matters if it’s a good primer/sealer. I used etch primer in the bare steel and then feather fill (gray) then based with a chipped color close to the Portuguese until I had coverage then used the Portuguese over that so as to make sure I had coverage. The VMR (paint ordered off the internet,base coat) is pre-reduced and ready to spray and doesn’t cover well. I used almost a pint to do the fuel tank and the oil tank even after basing it with something close from a local paint store. 

I'm pretty sure it was white
 

Thank you both!