Rust repair on 1960 Catalina

I just picked up this Catalina and it is pretty solid minus the rear driver side where the body mounts to the frame. The frame is solid, the body sheetmetal is pretty well gone along with the trunk pan. The trunk pan I am replacing along with the supports under it that hold the fuel tank on. I am not sure what the easiest way is to make this repair. Any suggestions?
The pics arent the greatest, the car is outside and its dark. The pics are taken from the driver side looking in at the rust. It is right behind the rear driver side wheel.

punisher7 said:

I just picked up this Catalina and it is pretty solid.

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Nice! 389?

Rattler

It will have a 389 in her by the middle of the month. It came with the tranny and I just picked up a 389 out of a 64 Cat. Can't wait to get her on the road!