I have the Milenco Grand Aero mirrors. No issues with the clamps touching the mirror glass. We do place some 'anti-slip' material (you may use this in the drawers of your caravan, to stop glasses etc from moving around) between the pads of the clamps and the mirror housing, just to give the mirror housing some protection from the pads (it probably doesn't make much difference TBH).
I also tether the mirror arms with stretchy straps to an anchoring point under the bonnet. This prevents blow-back by passing road trains, and reduces some of the vibration you may experience with the mirrors.