Assuming you have the same plastic fridge vents I have, I can see where hard-driven rain on that side could get in easily. Those vents are not really laid out to keep rain out under those conditions. Its good you discovered the water quickly.
A somewhat worse problem around here (desert Southwest) is the fine dust that coats anything semi-enclosed--like the interior of the fridge compartment, the water heater, and the rear bumper storage. THe rear bumper storage has a surprisingly thick coating of dust over everything---to the point I'm seriously considering some big drain holes so I can stick a hose in there and flush out the dust...
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.