I didn't know this was so widespread, this is my easy fix from a few years ago, so Softail owners take note:
A picture is worth a thousand words, here they are. Take the positive lead and turn it horizontal. There is no way the lug will make contact with the oil tank frame in this position.
As another measure, (which really doesn't relate to the problem) is to put silicone over the TOP side only of the positive terminal. It prevents fireworks should you drop a wrench on the battery; and no I have no first hand experience with that one, close though.
Bonus is the cured silicone is now transferable to a new battery if you elect for the same HD battery when it's time for a refresh.
