My paper towel holder is mounted just aft of the passenger's head on the
inside of the curtain track on my '85.  It's reachable by the driver,
the passenger, and by anyone standing outside by reaching up through the
open slider door.

I keep the towels from unrolling by "Sandwiching" a piece of metal
between the holder and the curtain track.  This metal is bent at an
angle more acute than an "L" so it maintains pressure on the paper
whether the roll is new or down to the last sheet.  I don't have to
think about it and it works beautifully.

Mike
'85 Westy 2.1