I battled that wet compartment for several months. My final solution was to run over every outside seam I could find with silicone caulk, fingered in. When I had reached all I could reach, I got a can of spray-on undercoat and went over all the outside seams. The spray could reach some areas I could not reach with a finger. BEFORE you start spraying that stuff, mask off anything you don't want to overspray, like tires, shiny chrome wheels, and the side of the coach. If you do make a mess, personal experience let me know that WD40 will clean the stuff up.
Dave & I have very similar coaches, but totally different side mirror setup.
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Paul (KE5LXU) ...was fulltimin', now parttimin'
2022 Coachmen Leprechaun 319MB
towing 2017 Jeep Grand Cherokee Limited