Does anyone have any tips on repairing this rust? It's in the driver side rear wheel well.
Should I just wash it out bomb the inside with that "rust converter". Then weld the outside.

Any other ideas that don't involve me drilling out 3/4 of the spot welds in the car?

 

With the POR-15 product, you need to clean the loose scale, grime, grease, and dirt off, hit it with the metal ready, and then you paint over the rusted metal and it's supposed to cure and prevent further rust. There's discussion buried in a lot of these threads about the pros and cons of POR-15 in general, but I think you'd be hard pressed to get at that rust and properly treat it with POR-15, or any product, unless you can get access to it all and clean it up properly.

That said, the only really bulletproof way to beat rust is to cut it out and replace it, and to do that you'll have to drill out the zillions of spot welds, and have a rust free piece to replace it with. That's what I'm going through right now...