hello all,Im for the land of the froozen north and need to know if the stock heater will keep me from freezing at 30 below.the cab is a 52 chevy 1.5 ton, it will be setting on a 77 4x4 daully frame. If so will need to find a complete heater unit,and if not what is avaible? any thoughts would be of great help.THANK YOU