Here is a quick little tip for repairing a power or tow cable where the outside jacket is slowly pulling away from the plug.
Fellow full-time RVers Greg and @Lorraine clued me into this repair. First, you heat up the cord either by leaving it in the sun or with a heat gun. Next, add some brown Gorilla Glue or another similar adhesive (I used G/Flex Epoxy) to the end near the connector.
Then slowly pull on the cord, working the cover toward the plug end. Eventually, enough cord material will shift forward and back into the plug. The glue or epoxy will seal it in place, preventing the problem from happening again.
I actually had taped it before and over time it still slowly pulled away. I think the trick is to get the existing covering back into the plug head where it starts out when new along with some glue so it seals in there and doesn't pull out again. Other cords I've used have a physical clamp inside the plug, but these are molded together so can't open. Could have always cut the cord and added a new plug but this was simple to do.
For my 30a. shore cord I just replaced the plug. Incidentally, I found a very good quality replacement. It has chromed-type lugs that seem to dissipate heat much better than the original brass ones did.