I just hate the design of that lower fridge vent (the plastic Dometic part) and the Chinook floor there (Chinook). It's like a leak waiting to happen (only waiting until the first rain
) Can we even count the ways it's a problem?
1) The Chinook body slants slightly inward in that area (sporty), so the vent is already at a disadvantage.
2) Sure, the vent holes are "upside down" to try to prevent water ingress, but where the removable part joins the fixed flange, there is a gap all the way around that is not "upside down." Sure, water, come on in! I don't believe there is ever supposed to be foam around the vent door - I bought a brand new one and it was the same as the stock one (Dometic product). Just plastic that you bed to the body around the flange but nothing at the door/frame interface.
3) The Chinook floor there is below the bottom of the vent vs. being slightly above it. IIRC the instructions from Dometic show the vehicle floor being just above the bottom of the vent, and slanted outward (i.e. they know it can leak and the RV builder is supposed to account for it).
4) There is nothing there to account for water coming in and divert or direct it (I think on later models they threw in the towel and made a fiberglass pan there maybe?).
My Chinook had been kept indoors, so there was no sign that water had come in there, but as I didn't want to camp indoors -- and I could see the potential problems -- I wanted to do something.
I initially made a diverter at the bottom of the vent. That did work (although I was in limited rain). Not sure if it would have allowed enough air to the burner of the stock fridge or not. If I had been going to keep the absorption fridge, I would probably have kept the vent stock, then removed the fridge and made some kind of fiberglass pan - perhaps tying in with the fridge condensate drain - that was designed to accept and dispatch the inevitable water ingress.
However, I already knew I was going to a compressor fridge, and one of the plusses to my mind was being able to close off that lower vent (even if one did want to have a lower vent, it would not need to be that design since there is no longer a fire burning back there once you don't have an absorption fridge). So I never made a custom pan.
Some people have run a bead of caulk as a "dam" on that floor - not sure that really diverts the water to a better place, although if it's just a few drops I guess it can just stay there and evaporate. On my Chinook there was some of the leftover vinyl covered "paneling" pushed up against the outside wall (on top of the plywood floor) and caulked to the outside wall. That worked for nuisance drips.
In contrast, I have never had ONE DROP of water come in the roof refrigerator vent. Much better design. (And I would know as since I removed the absorption fridge, that upper vent has been above a small cabinet so any leak would come into the cabinet). I've been in some wild monsoon storms with that thing. However, that's not to say that if the bedding got old, it couldn't leak around where it is bedded to the roof. If I had leaks in that area I would re-bed it just to be sure. But I mean the vent openings don't leak. Too bad the lower vent is not as good a design.