I made two of these, one on each side of the boat, for my Santana3030. It took one visit to REI, about $25 worth of climbing webbing, and 45 minutes with a sewing machine. Now, mine might not have supported 6,000 pounds, but you know...I'm OK with only supporting 1800 pounds.
Suggestion...if you make one, double-up the webbing on the bottom of the foot loops. That makes them stiffer, so they stick out from the central strap. If you don't do that, the loops tend to collapse, making it hard to get your feet in them.
I used a substantial s.s. carabiner to fasten the thing to my aluminum toerail. Then I lashed it to the stern pulpit with really light line, set up with a quick-release pull.
1968 Selmer Series 9 B-flat and A clarinets
1962 Buesher "Aristocrat" tenor saxophone
Piper One Design 24, Hull #35; "Alpha"