Isn't something like Dupont DP-90 or some other primer/sealer the only kind of primer that is weather-safe?
Rattle-can primer is probably better than nothing, especially in more humid areas of the country where even sitting inside an enclosed garage will end up flash rusting.
I'm spoiled, I'm in a dry climate.
But I've been told you can use spray can primer so you can work on your project and block sand to see your low spots, but then you'll have to go over it again with good primer prior to paint.
