Horribly expensive oil based paint works fine, as you've discovered. So, too, does the cheap stuff when you run out of money. Most hardware stores sell Rustoleum or their own generic brand of rust inhibiting paint. {Not talking about spray paint} If it thins with mineral spirits or paint thinner (rather than with water), you're golden.
Porch paints have always been an option, too, though they rarely dry as quickly.

Good luck!
Dave

BTW, I have used plenty of spray paints on SOF boats - but only after I have base coats applied.