MF... Couple quick notes... I am envious of your ability to store in your driveway. I suspect you are very much in the minority. I am fotunate to have gated storage 20 minutes from home and a busy active lifestyle means I am not always in a position to check my rig on a weekly basis, let alone a daily basis.
I am not sure I can agree with your evaporation theory. But if it were true, that goes on to support the secondary reason to cover, UV damage. For the evaporation to occur you would need full sun on your rig. If you are like most Canadians, myself included
and your rig is parked from late October to Early May why not protect it from damage. If you owned a $80,000 corvette would you leave outside exposed to the elements???