I put a maxAir cover on our Sprinter based B. I used a Fan Mate which attaches to the fantastic fan surround. Its nice to be able to leave the fantastic fan open and not worry about rain. The fan does't open all the way inside the cover, but so close that I don't notice any real restriction in air flow.
I installed it by using a ladder on the side of the van and didn't have to get on the roof. A Sprinter may not be as wide as some Bs, but is taller.
I like it. I think it offers some protection for the AC unit on the roof. It hinges open for cleaning out if needed. The mounting holes are in the Fantastic Fan surround, so no real noticeable additional holes (there are 4 new screws, but they are covered by the fan cover and are not outside the footprint of the fantastic fan base- if you removed the fan cover, just replace the screws with some decor and it looks as nothing was ever done).
The only downside we have found is that if the fan is open inside the cover, and we are driving with the van windows down, the suction of the cover will make the fan sound like a jet engine. This is to say that with a lot of air moving into the van the fan will freewheel maybe faster than it was meant to spin. The solution is to close the van windows some, or close the fantastic fan cover inside the MaxxAir box.
One of the best things I have added to our Van.
Bob