Should/can I seal the back of this camper to keep leaves and water out of this groove?

I'd probably just buy a cheapo cover-- and at least keep it on for leaf season or when it won't be used for a while.  I don't think you'd have much luck with sealant back there-- too much of a gap and too much flex with travel. 

We had a 320 in a super humid area too (and kept it covered).  We kept a cheap dehumidifier inside (I ran seperate power cord just for the dehumidifier so I wasn't powering the whole camper - ran it through an opening in the nautilus box).  You can put the dehumidifier in the shower and not have to worry about it leaking, etc.--- just open your gray tank and let the dehumidifier empty down the drain.  Honestly, I would do this regardless of where I lived (except maybe the desert)-- just nice keeping it 50% in there.  And really, unless you have the cover really tight, enough air gets under there that we never had any mold or mildew on the outside of the camper either.  And the outside stayed cleaner.  Just one thing though-- you'll want to cover your windows with some saran-- some of the covers will scratch that lexan.  

HappyCamper2024 said:

We live in a really humid place and the general consensus seems to be that  a cover is a recipe for mold. The leaf fall is several months, so that would be a lot of cover time.

Thanks for the info on the sealing. My only thought is that it doesn't have to be perfect to keep leaves out but I guess it could allow water in and prevent it from evaporating. Maybe I should just put some masking tape over it and remove it when we travel.

I live in Florida and use a cover whenever we put our t@b in storage.  The cover is loose fitting so air can flow under it.  Our t@b is a 2019 and looks as good as the day we brought it home in 2019.