Why you should not put a Cover on a Fantastic Fan.
There are a few different models of Fantastic Fan..Some of them have electric motors that raise and lower the cover. At least one you open and close by hand.
The problem is the covers, are NOT large enough to allow you to fully open the cover in many cases (MaxxAir II may be, Not sure) and this can lead to cracking of the lid.
If the FF is an automatic (Powered head) model the cover prevents it from sensing Rain.
And in all cases the cover CAN restrict air flow...Slightly.