If your stick-on RV mirror gets knocked or falls off, don't bother wasting big bucks on the $10 a small tube "use a bit toss the rest" type of *specialised* adhesives.
Try not to disturb the residue of the old adhesive by scraping, instead give it a wipe with a clean solvent (prepsol, acetone or the like) and grab a small tube of good quality Super Glue as it has the same base material as the *specialised* type.
Wipe a light coat over the glue left stuck on the windscreen and the same on the mirror mount, wait a few minutes until tacky & restick. This way you reactivate the original acetone base adhesive & get it to return to a liquid momentarily.
At worst, buying a new tube of Superglue may cost $3 and if there's anything else around needing gluing as there usually is, you can stick that up before the rest of the tube goes off.
The Specialised stuff usually comes in too small a tube to even think about doing that & done correctly is no better than this system.


Alan S