We installed a MaxxFan Deluxe model in our build. It has a built-in Rain cover. Considering that we have been rained on during every camping trip this year, it's performance has been outstanding.
We rented a Little guy trailer last year that had a Fantastic Fan and when it rained the first night we had to close the fan, not a comfortable night!
After that we made sure there was an awning over the trailer, it was a PITA. The Maxx Fan Deluxe is more expensive, but we found ours on sale for a reasonable price. I know the Fantastic fans have quite the following, and if you already plan to have the trailer under cover or if you camp in arid climates it should be just fine.

MaxxFan closed

MaxxFan opened. (I guess I need to open it when I wash the trailer, it looks like I missed a spot.)
I hope this helps,
Dr. C-Dawg
