Have you tried the V shaped (in cross section) strips of plastic or metal? They don't have insulation value, but they are springy and will condense or expand the width of the V depending on how much space needs filling and so stop drafts. (see link below) You could maybe use this in conjunction with tacked on (not just glued on) foam strip if the gap is really wide. There is also a type of weather stripping that is tubular and sort of tear-drop shaped in cross section that might fill the gap.

Is there some type of a rubber type of flap you can put on the side of the door jamb that the door closes towards in addition to the V strip? Perhaps with magnet strips on the the door and the strip so they pop together when the door closes? I know that stick on rolls of magnetic strips are available at office supply stores.

Here is a link that might be useful: V strip weather stripping on second slide

A couple of questions on your door:

1. Have you determined why the gap varies? Is the door warped? Is the frame warped? Both? Figuring this out may offer some clues about what you need to repair.

2. You mention that the gaps change with the weather. That would point to the door, frame or both not being sealed (paint, oil, stain or whatever) adequately to prevent them from absorbing water and changing shape. And possibly that you have water leaking in on the door or frame. Fixing this would likely lessen the changing gap problem.

3. You don't mention what sort of jamb you have on the door. Is it a standard door jamb? interior or exterior? a homemade one? And how much wood overlaps the door when it is closed? If there isn't sufficient overlap then it can be hard to get a good seal or apply weather stripping.

Take a look at a fairly modern front door sometime. They generally have about 3/4" of wood overlap at the door edges. Interior doors (which are not designed for weather) generally have about 1/4", just the tacked on door stop strip.

Once you know the answers to some of these questions, it should be easier to see what changes you need to make.

Is it possible to hang a couple of heavy cloth "curtains' inside the door? Furniture-moving-pad heavy, sliced in long strips, a bit like those clear plastic slit curtains on loading docks that forklifts can drive through.

If you can't put weatherstrip between the door and the jamb, nail some rubber garage door bottom to the inside of the jamb framing so the door pushes flat into it when closing. Nailing something flexible to both the door and the jamb also works on the hinge side, cutting infiltration by 25% immediately.

Agreed that a good remedy would be to even out your door and jamb edges and seal the wood bigtime. Got any aluminum or iron angle hanging around to frame those two things? They then become the actual doorway and the old wood door becomes filler material.

Wow, lots of good ideas! Thanks. Some type of cheap cloth curtain seems the easiest fix.

Another idea that came to me was to try caulking again, but first line the edges of the door with masking tape or some type of non-porous plastic, then apply a thick line of caulk on the surface where the door meets when closed. Immediately after caulking, close the door and latch it. Wait a couple of days, then open the door (which hopefully will not have stuck to the caulk). Will the caulking have dried in the correct shape to fill up the odd-shaped gaps?

Use