I tried my modified anchor system out last weekend in 16 knots of wind and it worked a teat with a big lifter and 3 laundry (10mtr Killer whale, 10mtr Panda and a 10mtr tiger) attached to its line.
I could let out the 9m2 lifter to full height just by running the line through my fingers, using the red "figure of 8 descender".
The old grey seat belt I attached into the Reece hitch receiver of my Patrol using it's cross pin with the tongue removed. Worked well as when the wind changed I just rotated the vehicle by letting the hand brake off and they pulled the 2.5 ton Nissan backwards on the soft grass.
Kept it all tidy and made it really easy to retrieve it all when packing up in a strong sea breeze before dark, so I made a second setup today.