A sheet of adhesive backed paper works well for making a template. With the
adhesive still covered and facing away from the door pocket
lay it over the backside.
Using a couple small nail especially
if you have a small roofing nail that will fit flush each into each screw
hole. Push these thru the paper into each screw hole. Use some tape across
the head of the nail to hold it in place on the paper. When you flip it
over so the door pocket is now facing you the nails will keep it lined up.
Trace the outline of the pocket on the paper.
Now set the pocket aside and cut the line you just traced. Pull the
adhesive backing off. The nails taped to backing come off with the backing.
You now have a template you can stick in place. If your careful and dont
press it into place. It will be easy to position it where you want then
smooth it out.
Remove it after marking your screw holes or drill thru it. I would also cut
a very small x into the vinyl with an exacto knife before drilling at each
screw location. Even better a small circle just bigger than the screw. Only
to prevent the vinyl being torn while drilling.
I have used the adhesive backed printer paper and it works out well.

Bill