There is a really good finish comparison done by Mar-K. You can see it at
http://www.mar-k.com/wood_finish_testing_ii.aspx Follow it through the 2010 update.
Clear coats did not fair very well in the comparison. Probably because the finish is not made for a surface that can change as much as wood under different temperature and humidity conditions. Marine spar varnish did well.
Chuck
