I have a Blue ox coiled electrical cable that runs from M/H to Toad. I purchased it in 2010 from Blue ox. I have noticed that the outer covering of the cable has many cracks from one end to the other....
I really wouldn't worry about its cracking. Other than cosmetic, the wires inside are also insulated so its not like moisture is going to get to the wires and corrode them. That cord will be useable long after you retire it.