FishB8s,
A couple of thoughts, one new, others "old".
We have an 08 PW Lexor with a Fantastic Fan. It was delivered with a three speed reversible fan with manual control. Reasonably early on I swapped the "guts" for their remote controlled, variable speed, temperature controlled "upgrade". It included the rain sensor feature. 'Twas a very easy install and completely from the inside.
One of the times we like to use the fan is on a mild evening, until it rained. Then the lid would close, and the fan would shut off. Darn.
So, I added a MaxAir vent cover. I did have to measure very carefully as our TV antenna was "in the way" for some of the models. In the end, we could only use their "one rear opening" model, though I would have preferred their "three opening" (I think that's the Deluxe) model - but it wouldn't fit. You can find dimensions for all their products on their website.
I'm quite sure that the vent cover with the fan on the "outside" is MUCH quieter - as others have said - but I wasn't willing to take on swapping out the whole kitandkaboodle as we're happy enough with what we have.
Now when it rains, we simply use the fan as we wish.
Separately I agree with Rodger (My Roadtrek) and others about supporting Fantastic Fan. Yes they were sold, and things may have changed a bit, but I'd still support them as they've been good to us.
Finally, if you're installing a "cover" over an existing fan, I'd encourage you to spring for the optional "opening mount". Since the Lexor roof is curved a bit (unlike most Cs and As), it won't fit flush and you'll need to either "open it" (from the side) if you use the extra mounting kit, or you'll have to remove it periodically as I'm continually surprised about how much "stuff" gets under the edges and works its way toward the fan. I open it and clean it at season's end before winter and then check it again in the spring - just 'cause I'm a bit anal about stuff like that.
Installing the cover does mean getting to your roof and requires some drilling, but it's not hard if one measures carefully.
Cheers.