Ken, in all seriousness, don’t entertain the idea of nitrate dope over the Rustoleum. Only bad things can happen.
You have a big plane, so another complete coat of primer that you don’t intend to sand off is going to add weight you don’t want. Exactly how much weight is difficult to say, but probably at least a half ounce. So if you REALLY think you need a lockdown coat, do it thin as possible with Rustoleum. Maybe even Rustoleum clear since you don’t need fuel proofing for electric.
If the model is ready for color otherwise, My advice is to clean the model thoroughly and go right into your base color and go from there. Hope it works out.
This is what I was after. I have never had the pleasure of a non dope finish (I have been doing this since about 1955) so I am a rookie at this. My routine was simple. Tissue on the fuselage, silkspan on the wings. 4 coats of clear, sand with 400 till smooth then start adding "X" filler coats (dope and OMG Talcum Powder) until all of the low spots were filled sanding all of it off with 400 except where it actually "filled". One more coat of clear with a bit extra where there was an abundance of filler and all of this was brushed.. Wet sand with 600, let it gas out a couple of days and go to color. Life was good.
I should have stayed with this but the only "Dope" at our local hobby shop was the guy behind the counter so off we go to Home Depot. I used pollyspan since there was no more silkspan (I found out later you can get it if you have good credit) . Really easy to cover but lord help you if you sand into it. 4 coats of clear and everything looks good. I used gray Rustoleum filler followed by white Filler/Primer. I am not sure that the Primer is the same base as the Rustoleum color but it is compatable. If I go to color directly I will be hitting places where I am sanded down to nitrate or z-poxy. That is why I wanted another coat of primer in my base color (white). However, enamel should stick to all three so maybe I don't need the primer EXCEPT that I still don't have a consistent base color coat to examine for and correct flaws. I fly them at this point and I have already flown this one. It resulted in major surgery to correct control issues. The scars from the surgery look and feel like they are covered but you don't "really" know till you hit them with color.
That is a very long winded explanation of why I am conflicted over what to do next.
1/2 oz is still in my weight budget. I have 8oz to go before I have to register with Weight Watchers. 6 is my goal. I am guessing that color is heavier than primer. 2 coats color, three coats clear. The good news - next time won't be the first!
This is my 1st .60 size ship and if the test flights are any indication, I will be able to easily make up the 5 points or so I give up on the finish by the time I am done with the loops.
Thanks - Ken