Okay, just finished vinyling the front door of my ROTJ and I think I have the secret. This was using Rich's matte black vinyl, which to me, is pretty thin and stretchy. I used it on the front of my 720, which took me 2 times to get right, with the second time taking me 45 minutes just to do the bottom 4" using a heat gun and going 1/8" at a time.
Today, I didn't push as hard with my squeegee as I have in the past. I was actually really gentle...just enough to tack it down firmly. After trimming the edges, then I went down over it with more pressure to get the best adhesion. I had a lot of vinyl left over (and still do), so I had vinyl to waste on the front door. There are 3 keys:
1. Only work about 1/2" at a time and don't remove too much from the backing at a time. It's the backing that keeps the vinyl firm, and prevents your squeegeeing from stretching it.
2. Don't pull it tight. I did that with my 720 and thought that would prevent air bubbles. All that does is stretch the vinyl and create vertical ripples.
3. Don't push too hard. Just gently wipe vertically and don't work the edge around the coin door hard. Be especially gentle at the bottom edge of the coin door. Once you have the entire front done, then you can go back and really push down around your edges before trimming everything.
Different things work for different people. I may get pics up eventually, but for reference, ROTJ has a double vertical coin door with nothing separating the two doors. Now I've got to go back and trim it now...