I tried on on rear window of my last RV (2000 Infinity)... Really never worked well... I didn't bother to remove it when trading in.
For the sides - I find properly adjusted mirrors leave very little in way of blind spots. Each side (on mine) has 2 mirrors - a 'fixed' convex - and adjustable flat.
If adjusted, you should see a car in one of the two mirrors right up until it is at your side windows. (Some people seem to keep the mirrors in too far - wanting to see far too much of the side of the RV in the 'flat' mirror.)
Link to State Farm site on adjusting mirrors:
I use this for the 'Flat' mirror - the convex then shows even more...
The side cameras don't show me anything I can't see in the mirrors...
Rear camera is nice - but when towing just shows the toad.
Of course still have to judge how far back that car you see is - especially if towing too.