I have had a Yakima system on my Snug-Top fiberglass shell since 1998 with no problems and no leaks. Loads have been heavy enough to collapse the crossbars (too much lumber) and still no leaks and no cracks, just badly bent bars. The Yakima towers that I used fit into tracks that get screwed to the shell with backing plates inside, and the towers are designed to pivot on their mounts, so when the load collapsed the bars, the towers just leaned inward a little to compensate. When I installed the tracks, I pumped the screw holes full of clear RTV silicone to seal them. Have had a similar system on another truck since 2005 with no issues.