I have done 2 driver´s door seals. I began at the top of the vertical section of the A-post, where I applied some contact glue to secure the flat, thicker part against the lower end of the leaning part of the A-post.
Then as just suggested I worked my way up/backwards. The seal then needs to by cut by about 2" as it is too long. Allow for a little shrinking when cutting (which is hard as the base is stiff).
I had a few issues where the hard, plastic base wouldn´t settle properly on the near/outer side. When pressed harder, it deforms slightly making it even more impossible to push in. The soft part covers these spots, and I ended up leaving them, rather than trying to pry them with screwdrivers or whatever. I wasn´t entirely satisfied, but have gotten over it.
The entire lower section is very easy. The s/s instep plates need to come out and also the top of the "B"-post end requires a bit of fine tuning to get right. Altogether the new seals make a great difference, noisewise.
I agree that my thumb got a severe beating.
I will someday do the other sides (and the other cars). I like replacing the vent. widow seals too. And of course the vertical seals on the rear quarter lights.