You've gotten a lot of good options. I'll add just one thing that will maybe keep things in check awhile longer. Any place that you can access the area behind those bubble you should take a look and see if you can see any moisture building up or sitting in contact with the metal.
I've seen door bottoms rust out from the weep holes being blocked. I even had a car once that I kept hearing what I thought was gasoline sloshing around in the tank. I eventually had a look around and discovered the passenger door was about 1/4 full of water! A quick inspection showed thw slotted weep holes were plugged and I ran a hacksaw blade in the slot and water poured out for 10 minutes!
Once any areas that hold water are drained, or weep holes are opened, then you can address the inside. Rust neutralizer on the inside once it's dry, will slow the problem down, and allow whatever patch you do to last longer. After neutralizing, you can paint the area with Rustoleum to keep things from rusting again right away.