I used a full 5x4 sheet when I did the "Redneck Edition" and had about a foot left.I did not do the entire tank but did parts of the hand guards and the fuel canistors.
The vinyl will not adhere well to the Clarke tank. The fuel leaches through and bubbles will form between the tank and the vinyl.
I applied vinyl decals to the clarke tank on my 03 and it wasn't long before they bubbled.
As far as how well it holds up I just finished mine and cant comment although it seems pretty tough.