I don't blame you for caving on the superfly, good buy.
FWIW, its transformed my hanging. No more face rain, gear stays dry on the floor, much warmer. Works well on the horrible ground too.
Its a good simple project to do though James, well worth the effort while you are waiting for customs to come back from the woods with your tarp.
You dont need silnylon/spinn either-my doors are made from uncoated 0.9 oz parachute nylon and then soaked in TX direct. They cost me around £5 in total.