'64 custom body repair advice

I have a 1964 custom 2 door sedan. The body is in really excellent
shape overall EXCEPT right behind both rear tires. The bottom of the
body is pretty hosed back there, and on the passenger side there's a
bit of it missing!

I'm no body man by any stretch, in fact I'm just getting the car bug
to begin with. How do I go about repairing this? If you recommend
parts please mention where to get them, I keep searching the internet
to try and find something like a repair panel for this and just can't
locate it.

Thanks in advance, Mike.