We discovered water was getting to the lower wall cavities of our 2016 high roof last fall. We use those cavities for storage, so letting the water keep flowing through to a drain hole wasn't really optimal. In addition, we have shelving in front of the walls, making it hard to get to all of the trim attachment pins, to seal them. But I could get to quite a few. I also sealed all of the possible leak points on the roof, since it was easy.
I used spray talc (jock itch powder, I think) on the walls, after sealing the obvious ones, and checked it after the next bit storm. It was clear that water was coming in from a couple more, so I sealed those as well. But since I could reach them all, and this was clearly going to be a game of whack-a-leak, I decided to seal on the outside.
So this spring, when the temperatures got better, I ran a bead of caulk between the body and the black panels, all along each side of the van. I remembered not to seal the gas filler door shut. ;-) I'll keep checking the cubbies, but I suspect we'll be good from now on. Even if the caulk seal opens up a bit, as long as its not everywhere, and as long as it's not the whole gap, water probably won't make it to the pins anymore.
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The caulk used (both on the pins, and outside) was Sikaflex 221. That's "gray". Might use black if I had to do it again. But it'll get dirty, soon, and won't stand out so much. I'm sure someone else could have done a neater job, but the van is now old enough (6 years) that I'm starting to not obsess about keeping it pristine anymore.
paul