Not much room in the lower radiator hose to put anything. The cab heater line connects to the lower radiator hose on my BX23S, and you need to fight it just to get that small part into the hose and back onto the radiator. A Block heater is the only way to go.One possible option...
... add a lower rad hose style heater ?
I have no idea what 'access' you have,or how easy ,just thinking about options.