That's funny,the only time i ever had problems with a finish cracking was when i used e tex,not a single problem when i use devcon. :
Nothing i've found holds up to rocks and big toothy salt water fish better than devcon.If your going to test a finish there really is no better place than the ocean during bluefish season.
Most people that have cracking problems are either:
A. Not mixing it correctly
B. using an inferior substrate
C. Not properly preparing the surface
If your looking for something with the same general properties as e tex(ie thinner viscosity) but made specifically for the marine industry try System 3