KJ,

I have it on archery gear that is 12 years old it does not yellow or crack. I have researched it a bunch on boats its being blamed on UV but my guess is that it is more the expansion and contraction of large surfaces do too temp and moisture reuptake. Think about it. Wood is hydroscopic. You remove it from an environment that it has stabilized at 8 to 10% MC and stick it in the water and get it real wet. The MC doubles or more even on the most sealed surfaces. Then you put it back in an enviornment that brings the MC down again. I have epoxy based paints on metalic surfaces with no real issues that you see on wooden structures. Just MHO. I also think that you need to touch up the surface every year on rails ,oras etc that get dinged.