Unusual I would think on a 10 bag DP chassis.
Perhaps, the original owners had good success on previous rigs with the add-on stuff and just put them on for General Principle.
I have not used the systems, but they seem to be popular with folks who have handling problems on gas chassis.
1995 38' CC Magna #5280
C8.3L 300hp Cummins, 31,000lbs
Gillig Bus Chassis