Bedroom slide on my unit has Swintek side rails. Water wicked under the slide and rotted out small areas under the slide at the outside wall. I removed the rot and repaired the wood. It has the Darco wrap which is not water proof. I bought some thin aluminum sheeting from Home depot. (.085" I think) Used a box cutter to score several times and then broke it at the scored lines. Used heavy duty 3M double sided tape and attached it along the bottom side of the Swintek rail. I cut it long enough so that when I lifted the slide I could run it all the way under that slide. I then used Dicor non-sag lap sealant along the bottom between the new aluminum and Swintek rail and along the horizontal top and screw heads.
I read on another forum that a member found that the trim pieces on the 4 corners of the slide were not sealed and water ran between them and the wall and then down to the bottom. I removed mine, added lap sealant and reinstalled. I then ran a bead all the way around them. My other 2 slides have the rack and pinion. I noticed water wicking down the side and under them. I bought a piece of aluminum drip edge for roofs, loosend the screws and inserted it under the drip edge and caulked there. Good luck