Check out these mirrors
Brunsgaard Universal Towing Mirrors
They are made in Denmark, are extremely light and once set up take 15 seconds per mirror to put on. They do not move at all on the car, do not vibrate, have 4 points of contact and the size 4 fits the Discovery (4 point mirrors)
I have had 5 caravans, tried many different mirrors and have found these are by far the best and easiest to fit.
Drop them an email, they are great to deal with, ship them out really quickly and you can buy parts for them if required (I changed tug and brought just the 2 different size arms I required)