You may want to rethink the placement of the tank.
I don't have any problem with a tank in the cab as long as it does not leak and the hoses are good.
Think about it, where is the tank least likely to be damaged? In the cab, or at the rear of the truck when someone runs into you?
Perhaps inside the frame beside the driveshaft but in front of the rear axle is a good place too, but I don't think behind the rear axle is any better than in the cab.
Grigg
