It depends on what kind of failure you are experiencing. I am not a chemist or coatings expert and hopefully a board member who is will correct my thinking. The main failure mode for clear coatings is either separation from the wood or breakdown due to UV exposure. Clear (unpigmented) coatings have UV absorbers to protect from sunlight. Being an "absorber" it will eventually break down from UV exposure and not be able to absorb any more UV and it begins to pass the UV through to the wood. This will deteriorate the wood as well as the finish and it will occur even if a primer/sealer is used. Any transparent coating will need to be refreshed every now and then to maintain the UV protection. The nice sailboats and yachts do maintenance coatings every few months or maybe a year at most when they are in full exposure to the weather. If you are only seeing darkening or dulling of the finish, sanding and recoating may be all that is required to replenish the UV protection. You did not mention what kind of failure you are having with the bed wood.
Smith and Co, the supplier of our CPES epoxy, has a good article on their site about making finishes last in the weather. I don't have their website here now.
Mar-Ktech
