Sorry if breathing life back into this thread bothers anyone, but I only found it about a month ago and ABSOLUTELY loved the idea. At that time I was putting together my DIY hammock and thought this would be a great opportunity to try the NHSS (No Hardware Suspension System, sorry grizz, your name for it was just too long) I retrofitted my whoopie slings by tying a cobra knot through the fixed loop. I then made 2 12' dogbones with an adjustable loop at one end.
The dogbones were then larksheaded around the hammock below the whipping with the adjustable loop free. In the picture, the pink cord is mason's line I use to help in opening the loop.
The SRL was made with adjustable loops at both ends so it would go over the cobra knot and then tighten down. With zip knots on the adjustable loop of the whoopie sling, it was a very secure system.
I have a friend who always has difficulty with the marlin spike hitch and I showed him the zip knot trick and how it secures the whoopie sling to the MSH. I think he'll be using it from now on also.
If anyone is interested in retrofitting the whoopie sling with a cobra knot, let me know and I'll post pics or a video.