I tried several finishes on different parts of a kayak frame about 10 years ago. Then left it out in the sun, rain, and snow. The canvas rotted away and paint and varnish have cracked and disappeared except in areas that I gave a single coat of epoxy to, and then a coat of varnish . Probably 2 coats of each would have been even better.

Night and day difference between the aging of the areas simply varnished and those adjacent areas covered with the epoxy and a single coat of varnish. While the varnish has probably worn off by now those areas have a slight yellowing--probably from the epoxy yellowing--but otherwise look freshly cut. Areas protected only by varnish or paint are significantly grayed, and the wood has gotten brittle in those areas, too.

PGJ