Our 2024 320s BD came with a Maxxair Plus fan. It's a good fan, but we do need to keep an eye on the weather as a windy downpour could mean water in the trailer. The Plus model has four prongs on its rooftop mounting flange. These allow quick and easy mounting of a Fanmate rain cover. The cover is held on with four pins that engage the mounting prongs.
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Photo shows the two prongs on the passenger side of the fan's mounting flange.
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Above shows the Fanmate cover mounted with pins to the mounting prongs. The pins are self retaining.
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Another view of the mounting. Once you figure out the alignment, removing or mounting the cover is a ten minute job using a good stepladder.