I don't know how helpful they are, but here are the pictures of a trunk pan replacement
What you are looking at is the one piece of replacement sheet metal in the entire car (due to a leak at the rear window)
I have never done body work, but i looks like a lousy repair job
what they did is to cut out most of the trunk floor and then drop a pan in - the new piece (not clear if it is new...lots of pitting under the paint) has a good sized lip that overlaps the cut out inside the trunk - from there they bondo'd inside the trunk to even out the lip and used tubes and tubes of caulking underneath - it is all mostly rusted under the paint
I guess my questions are this:
should there be that kind of overlap? - if not, is the idea that the new piece fits exactly with the cut out and the 2 pieces are butt-welded and then ground down? if the latter, how to you keep the two pieces together to get tack welds on...are welding magnets strong enough? If it is normal to have it like this, I guess I will still grind it all down to metal and try to get all the surface rust out and then refinish
next, it looks like they plug welded the supports onto the understide of the trunk floor (the pieces the gas tank straps attach to) - on one side they plugged only one edge - again, tubes and tubes of caulking - lot's of rust under the finish - should i just drill those out and start over? - i notice that the ends of the braces are not welded on at all...is that correct?