On valleys and zims there is existing tower bolts to attach an insulator. We just bent a piece of 1/8" x 1" strap iron, about 8" long. Drilled 5/8" hole in one end to bolt on the tower, then put a couple 90 degree bends and bolt the insulator to the other end. Need to fab 1 mount for each tower. Start the wire at the first tower and run it to the last tower. Run a wire from the first tower to the fence surrounding the pivot (the smaller the area of the pen protecting the pivot, the less adjustment to retighten after every move. Use at least 3 twine ties in the first span. Use 2 or 3 twine hangers on the regular spans between towers more on rolling or hilly fields - 2 are enough on real flat fields.
Then run a wire from the outside tower to the perimeter fence. You must move this wire everytime you move the pivot - it's kind of a pain because the cows learn to push the end when the pivot is on. A good dog really really helps, and this daily chore really makes good dogs. I don't hang the end wire from the system but use electric fence posts and move them with the wire. Also I use a T post at the perimeter and move it with the wire. This outside span is going to get real tight and brake when you turn on the pivot before you can get from the pivot to the perimeter to unwire it. If you strike an angle that leads the pivot a little, the wire gets looser for awhile and gives you time to untie the wire before it breaks.
In time the cows will chase the end harder and learn the fence isn't on when the pivot is moving. You can move the pivot with the fence still hot when you face that deal. As always, the fatter and sassier and better you treat your cows, the more they work you on the end and duck under the wire when the pivot is on.
After you move the pivot, go down the system and adjust the twine supports - lower the wire where it's too high and raise it where it's high. I use a horse thiefs knot so the twine is easy to untie.
Good luck, we started doing this back in the olden days when corn bore would put a lot of corn on the ground and cows would overload on it if left unrestricted access. There is a tremendous amount of feed in an acre of corn stalks if the cows don't waste it and cows will go through a foot of snow to eat ungrazed cornstalks, but if they've been picked over a little bit, they'll stand at the fence and bawl if you get 4" of snow.