Back in the days of towing a camper with a 3/4 ton pickup, the kayaks lived on top of the pickup camper shell. They were covered for sun and rain protection, but I still had to put drains in them, because they would fill with water. Not really a difficult solution, but had to strategically drill the drain holes to get the water out. That was so I could get the kayaks off the roof of the camper shell. Yes, another one of those- "I should have thought of that first" moments. No harm, no fowl, but it was important to drill that 1/4 inch drain hole right where I wanted to put the 1 inch drain, in the low part of the hulls. Drains and plugs purchased at West Marine for Sunfish or Lasers.