Joe14580,
When I started flying 10 years ago I spent 3 weekends building a restraint system too. After a season or two it broke and I had to decide to rebuild it or find something else to use. I've found that a tent stake and a length of rope to be the best restraint that I've seen. It holds just about any size plane back without worrying of slipping. And it's priced right, about 75¢ for the entire rig.

Well, that's my 2¢ worth

Ken