Old air sells two cutoffs I would suggest you use. One is a manual cutoff to go on one of your hoses, the other is a cable operated valve that will adjust the hot water flow to your heater. That way you can adjust the heat in the cab on a not-so-cold day.

http://www.oldairproducts.com/catal...s/accessories-c-1_50000000_33000000.html


~Jim