I usually do the door channels, end of door and mirror bumper using the same custom bamboo skewer that newton does.
The door channels are the easiest things, why skip them?
You do need to be careful with the area around the mirror bumper. I'd remove the screen to be careful
Door channels really aren't that critical and thin yarn is best if you really have to cram something in there. Seems some sort of waxed yarn or cordage was used on my old F's body where the film back slid in--no foam in sight.
Putting a fitted piece of copy paper over the mirror to catch any gick has always worked for me.