OP - Lest you get the impression that having a Fantastic Fan with a rain sensor is an automatic problem waiting to happen - it is not. I have a FF with rain sensor and remote and have had no issues with the rain sensor at all even when the moisture content in the RV is high(er).
That is probably because it is under a cover. So why do I have a FF with rain sensor if I am going to cover it up? Only one post above came close to this point - you have to take the rain sensor if you want the remote and that was the case for me. My wife is short and she wanted to have a FF with a remote. I cover all my vents - automatically. Makes no sense (to me) not to.
So, if you have to get a remote then go ahead and get the FF with the rain sensor since that is the only way it comes. If you don't need the remote then I would not get the rain sensor model, given that you will be covering it up. The engineering of the rain sensor is not as bullletproof as a vent cover.