I'm just seeing if anyone would be interested in this.
I have made a 20 foot version and it gave enough speed for most flat and down rails, but a 30' one will definitely give enough speed for all rails!
The bungee's are 3 - 30' shock cords braided and tied off with a 30' lead line and one or two PVC handles
Pics of my 20' (minus the lead line)
Please PM me if you are interested!
Daniel