Is yours the crank that Urbane sells with the 110mm BCD? If so, I have the same one, and the CR bolts that come with it are really poor quality. I swapped them out for another set, but I can imagine running them in salt will make them difficult to remove. Pennetrating oil will help a bit. Also, if you have a pair of vice grip pliers, you can usually grab the chainring and spider in such a way that it puts the chainring bolt in shear. Often, this will give you enough torque to break the bolts loose.