Well finally got tired of all the dust infiltration in the back end every time I hit the back country. Was going to do this sunday so I am posting it but did it today. BIG hole right behind the mudflap on the pass side where you could not see it easily. Had to go dig out my 110v flux core mig machine since I have no 220 where I am right now, and got a chunk of 16ga for the hardware store, and made a couple of patch plates up, found 1/2 a can of hide-a-hack (3m undercoating) and that was that, total out of pocket cost on this deal 9 bucks for the plate of tin. Took me about 4 hours from wheel off to wheel on, and given I have not touched this welder in 4 years and have not struck an arc in 2 I dont think it turned out too bad. Hosed the inner fender down inside really well with Fluid film, while it was open. Sorry about the crappy cell phone pics.
Started with this
2016-07-26_09-40-10 by mrsleeve, on Flickr
cut out a lot more rust you can see about where the good metal starts in this shot getting back near the drain hole. Had to make a plate to put back there so I had something to weld the cap plate to on the end.
Ended up with this about 3 hours latter with a bunch of slag burns on my wrist getting between my glove and shirt (could not find my welding gloves). Not that bad for flux core and outta practice , had a big hole to fill on the right side. Yeah I knocked a BIG hole in it..... LOL Hosed it all down with Hide-a-hack put the mud flap back on and it should keep the dust and water out now lol
2016-07-26_09-39-20 by mrsleeve, on Flickr
Did you solve the water ingress problem that caused the rust through?
I recently went through this goat rope myself, and in the end, discovered that the welting below the window had worked itself loose, which allowed water to get in there, which is what caused the rust through in the first place. My fix was to pry up the welting, coat it liberally with clear 3M adhesive/sealant and reinstall it. Now it's dry even after the hardest rains.