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I would think that any of the kayak-type 'track systems' would still mount to the gunnel, even if rounded somewhat at the top. At worst, if the track is 3/4" wide. add a thin 1/8" wide 3M outdoor 'car trim' adhesive strip down the length of the track, to each outside edge ... not so much for adhesive, but to balance it. That adhesive is a good 1/32" or better thick (before compression) and would help.
