I've been having a run of composite canoes come in with broken or rotting gunnels.

Too many people treat wood gunnels on a canoe the same as they would aluminum gunnels. You can't. They need to be stored in a dry place and the finish needs to be kept up. This is not helped by canoe manufaturers who are hard pressed to make any money at canoe building and feel pressed to keep their retail prices low. So, to do that, they maybe get one coat of an oil finish on the outer surfaces of the wood. Canoe owners usually work with the assumption that that is enough.

Then the canoes come to me looking like this.