so when the channel fills up the water will overflow outside, not inside. Would also help to drill periodic weep holes on the outside rail so the water doesn't sit in the slot long-term, but don't count on weep holes alone, as they tend to fill up with dirt or just be overwhelmed by volume. I encountered this issue at the bottom of my slotted companionway on a prior boat, unless it was cleaned periodically. You may also get leaking at the ends of your tracks, unless you seal them well. It might become a maintenance issue if the structure goes through expansion/contraction or hull flexing.