I have a spray can of Minwax Fast-Drying Polyurethane that is supposed to tolerate glow fuel to a point.
Way back in my "improvising" paint job days I used the exact Minwax spray you describe here. It works, but with multiple compromises. It's safe to spray over pretty much anything, and tolerates fuel well, but after a time (and less than you'd think) it gets brittle and develops spiderweb cracks all over. Also, if you need to do any sort of covering repair nothing sticks to it. Long story short, don't give yourself more headaches down the road by using it.
In the case of your P-40 here, I'd suggest just repainting the entire model, ideally with dope. Better yet, hang it on the wall and build an all new one.