Regardless of whether it sticks or not or is fuel proof or not, you're going to also have the new problem of weight. Monokote adds a fair amount of weight by itself, but it's necessary to have the plane covered in something so we use it. It's lighter than any painted option, but not lighter than Koverall or Solartex that you would normally use underneath a painted finish. So someone has already added the weight of paint on top of the Monokote that was on there, and you've come back and added more weight by priming over that paint and plan to add another layer of weight with your color coat over that. Paint is heavy, and I'm afraid that if you go the route you're planning to go your plane is going to fly very heavy. You really should consider either switching to a fabric or glass base covering and painting that or stripping the whole thing and going with a straight Monokote finish. That way, you'll be saving considerable weight and dealing with all known chemicals and compatibilities.