I was thinking this as well, and definately agree some marking method will be needed to ensure a correct hang.
You could also use the tail of the "whoopie" to tie the ring in place when you take it down, but you'll probably still want markings. I was thinking of using a small safety pin, so you could easily change the marker location.
Also, for reference, I used 35 ft of amsteel for that rig. With a 8.5 ft ridge line.