I had a pearlescent black Cali until last year which I kept outside but under a cover. (The club shop sell the very same Maypole covers). If it wasn't under cover the birds would use it for bombing practice. Being black it showed every mark so I too was apprehensive at first regarding the use of any form of cover. I also imagined it would mark the paint work through abrasion however I found the Maypole cover to be excellent in every way.
My only criticism concerns fitting it. If it's windy, forget it.
You can just chuck the cover on top and then pull it about until things come right but I found that system didn't work very well in practice. Fitting it on your own has to be a disciplined affair. The first time you fit it, find a large expanse of clean floor space e.g sitting room floor and open it up so that the outside surface is upper most. The end with the three adjustable straps is the rear of the vehicle. Roll each side into the middle so that you end up with a long sausage (running front to back) with the inside surface showing. Then fold the sausage up remembering which end is the rear (the end with three adjustable straps). Then carry it out and plonk the bundle on the Cali roof. For this you will need a set of sturdy steps. Once on the roof unroll the bundle firstly towards the front and rear and finally down each side. Then adjust the cover so it is central on the van and then do up the straps that pass under the vehicle. There are three buckles on the bottom edge of each side of the van cover and three separate straps which connect them with their partner on the other side. To fit, just bundle up the long strap into a ball having first connected it to the buckle and hurl it beneath the vehicle towards the buckle on the other side and you should find it will be easy to reach from the other side. Once attached tighten to remove any slack. Then do the same with the other two straps. Next tighten the three rear straps to a snug fit. Note: The cover is designed to fit over a bike rack if fitted.
Fold and remove the cover in the reverse manner and pack away in its bag. It will then be ready to fit next time. If used correctly they are superb at keeping a clean van protected from bird lime, tree sap and dust etc.
Note:
1. It is better to fold the mirrors in before fitting.
2. Ensure that before you attempt to either fit or remove the cover, that the three under van hard plastic securing buckles on either side of the cover (for the above mentioned securing straps) are folded away inside the protective pockets. If they aren't you might scratch the paintwork.
3. Only fit a cover to a spotlessly clean van otherwise any dirt will scratch the paint.