I had to replace the cargo floor around the interior wheel wells. I just used 20guage steel. I cut out the rusted portion. Laid it on the steel and traced it out. Cut that out and tacked it into place. Welded it all around. Ground it and painted it. You would never know it was there. Its relatively easy if its flat. If it's curved you will get to test your metal bending skills.
Good Luck
Lucas

86 Trooper II
Stock except for the Rust and dents that came with it. Restoration while being a daily Driver is in progress. Completed so Far-Front Brakes, Rear Brakes, Frame restoration, 1 1/2" lift shackles, custom front and rear bumpers