My plastic covers for the stern shower have disintegrated. The plastic is brittle and fell apart. These are only 2 years old and have failed, is this normal? Is there a sealer that I could have used and how long would that have kept it? Is there a stainless replacement? Also it seems that the dogs on the hatches seem to need some protectant to keep them from becoming brittle and decaying. I use a sealant but it does not seem to make a big impact. Any thoughts or ideas are greatly appreciated...