I had the wicking issue (Drops came down the side of the slide, over the metal rail then ran back under the floor. Costly Floor Replacement.
A year later I took a look at the slide during a steady rain...yup same thing happening. I saw this video and added a ski to that side of the slide.
https://www.youtube.com/watch?v=Lx8ouqlM5jo
I have 4 slides. Two have these SKIs and two do not-its a function of the slide design. This particular slide is the ONLY one where water does not drop to the ground but rather rolls back under the floor. I installed the ski per the link above and the problem is solved.
BTW, ski or no ski, if you don't caulk all the seams, screws, etc you can get floor rot. Don't ask how I know...