510 Mini-tub without a cage?

[HudsonMC]

I have some pretty serious rot in an area I'm not quite sure how to fix. I've included this picture of the driver's side quarter panel in front of the rear wheel well:

 

 

So, rusted through all three layers of steel there. As you can see, this rust extends up the fender lip, above the "boxed in" area of the rocker panel. 99% of the rust repairs I've read through only detail replacement of the "boxed in" rocker panel.

 

So, with the steel being 3 layers thick in that area, how does one go about repairing it? I've bounced around the idea of fiberglass BRE flares and the mini-tub per the "How to Modify . . . " book, but that's on a caged car. Can I perform these modifications without making the rear end of the car too floppy? The book only says to fill the fender gap with a panel attached with pop rivets and non-hardening body filler. I've got a 4-point roll bar that I could triangulate and weld-in if I need to. I don't have have the fab skills or tools to do much beyond that. The main hoop of the bar mounts just in front of the step in the floor pan, and then the braces going back hit each wheel well. I'll get some pictures this evening if y'all need them.

[skunk]

just cut it all off and get bigger wheels :D