I swapped doors from a parts donor to my caravel
recently and had a gap at the top right and bottom left with the new door installed. Either the old door opening wasnt "square" or the new door was tweaked, not sure. Either way the objective was to make the door fit the opening better. Mine was not bad, about a 3/8" gap in the two problem areas. I usually work by myself so I had to come up with a way to hold the door in place and work from the inside.
First, I removed the screen door. (this actually happened by itself when I was aligning it to the opening, the rivets ripped out of the hinge). Mine was held by seven pop rivets, so it wasn't a big deal. Then I removed the old door seal as I was replacing it anyway. After alligning the door for even spacing all around the edge (reveal) I spanned the door opening horizontaly inside at the top and bottom with two pieces of 1"X4" I had laying around. Any fairly stiff wood will work, 2"X2" or 2"X4" or even angle iron. I held each one in place using two deck screws through the board and into existing rivet holes in the door with the boards extending past the door opening on each side. This acts as a clamp to draw the door in by tightening the screws. As I tightened the screws I put shims between the door and inner frame the same thickness in six places, two at the top corners, two at the bottom corners and one in the middle on each side by hinge and striker. With the screws tight the door was postioned perfectly with even spacing all around. With all six shims the same thickness (3/16")the door is pulled in to within 3/16" of the opening frame leaving room for the new gasket/seal. I reriveted the inner panel with the clamp in place using new rivet holes and presto, door is now aligned.
I should add that most of the rivets on the inner panel were already broken or missing before I started. I should also add that I do not have pictures as I realized that I didn't have my camera AFTER I was baracaded inside doing the work.
P.S. It took almost as long to write this as the job itself but I hope someone can benefit from it.