Sounds like there is a bit of moisture ingress in the paint going on.
Due to the fact that I immediately repaint any vehicle I get with flat paint. I just get the sander out and take the offending areas down to metal. Apply some primer and cover it with flat black.
Then I am known for the flat black thing around here. I carry a bunch of different flat paints in spray cans in the back of my trunk so I can do a camouflage change up on the fly if SHTF. Flat black as the base and a case of spray cans for flexibility.
Just my thing really.
I do however suggest getting the sander out and getting the area down to bare metal to see how much rust is there.