Stig,
You need to hunt around to find a webbing that is not water absorbant like the original, thereby avoiding rust problems later on.
I used some strips of reinforced insertion rubber 30 years ago on my '25 and it has not squeeked or been any problem all that time. It is readily available in varying thicknesses or you can build the layers up to the desired thickness using thin strips. Once in place with a body bolt through them they will not move.
Another trick to save you getting premature ulcers, is to alter the thickness of each packing, as determined by trial and error, as a way of getting the final door fit correct. I have found that even if a body has perfect alignment prior to fitting to the chassis, it will distort when bolted down tight. Very thin packing strips can be made of a plastic, floor linoleum/ vinyl being ideal. The distortion is usually ever so slight but enough to cause doors to stick or misalign in the most irritating of ways.
Good Luck.
Geoff.
