how would you fix this door?

I would love to see these in person......AND they are POST door frames

And since they are showing only the back side I would say it was only the inner shell. Not the outer skin.

 

Well I figured the doors out. Those doors are for the NOVA body style. They are trying to make the NOVA style skylark the same. Which it is not.

 

Matt, I agree that the patch should be welded. Panel adhesive works geat for many things but a cosmetic seam is not one of them.
Also check the inner part of the door shell behind that, below the hinge. I've seen that area rust out before the outer skin.

 

I have effectively repaired this type of damage by marking the area, cutting it out with a cutoff tool (use tape to follow the cut line and care not to cut too low into the support metal). Then go to your local sheet metal shop and get a patch about 18-20gauge and shape it the same. I would probably use a step tool to step the panel and then weld in the gap - or as others have said, have it welded. I would remove the trim and be careful with the glass as to not damage. Getting and viewing the back of this before cutting is important. You'll also want to treat and possibly paint in there to prevent future damage. Need to determine why the rust developed in the first place. You'll want to ensure the back of this patch is treated and rust proof. also, check the drain holes to see if they are plugged.

 

I prefer to make the patch first.,lay it on top of the rusted area, making sure it reaches beond any rust that is visible inside the door by at least 1 inch. Then when the patch looks like a perfect replacement piece I will hold it exactly where I want it, maybe even clamping it with vice grips lightly in certain areas depending on the patch to ensure it is placed flat right where I want it. Then I will use a black marker to trace the outside edge of the patch onto the panel. After that I wil take a 1/32 cut off wheel and cut on the inside of the marker line. Then the patch should fit in there nice and tight. The patch may require light grinding on the edges to make it fit perfect. Then I wil butt weld it in place. Grindthe welds, spread some filler,sand/shape,prime.
After that the inside of the panel should be treated with primer or cavity wax or undercoating. Something other than bare metal so it doesn't start rusting again right away.

 

Very good detailed advise here, thanks all.
I havent torn into the project yet as I got held up with lots of work, keeping my daughter busy, and no real time out in the garage. I also MAY have a replacement door soon, so Im glad I put it on hold! if this is the case I might just keep the bad door and practice the repair anyways, better to learn on the rusted spare door than the one that will be on the car itself.