Do you have an Atwood or Suburban water heater? I'm guessing it must be a Suburban if you can get a socket on it.
I have not found an ideal tool for my Atwood yet. I wish someone would make a 15/16" stubby offset box end wrench (and sell it for less than the cost of a nice dinner out). Vice grips likely will chew up the end of the plug before too long.
Sometimes I find it helps in starting screws, etc. to turn them backwards a rotation or so before going forwards to get everything lined up properly and not cross-threaded, as Farmboy666 also suggested.