Update:
Mod is done, and installed.
Last night I epoxied on the cover to the wooden block, but there was a gap between the cover and the rubber seal:
So I got out the caulk (paint able):
After painting and attaching to the car:
from the inside and with new mirror attached:
I will see how this works on my trip this weekend and post up my thoughts.
I might get some testing data in next week.