I have the design of extension mirrors which are held onto my existing mirrors with rubber straps and location clips. I have never had any problems with these and believe that in part their success is the fact that the rubber straps flex and absorb the shock when they are hit by strong wind gusts. After 14,000+ miles of use I do not have any damage to the paint on my mirrors as I take the precaution of applying blue 3M Scotch masking tape to the top and bottom edges of my mirrors and also under the line of the rubber straps. This is a low tack tape and even when it was on for two months during our recent Alaska trip it was removed easily without any paint damage.
I have also found that to prevent the rub marks that you get on the sides and across the roof of your TM, particularly after very long trips, you should apply white 3M duck tape to the rub lines. This tape is very durable and can simply be changed perhaps once a year to maintain a smart appearance.
Geoff Card
2005 Toyota Highlander V6 4WD
2002 TM 2619
WDH