Any reason this wouldn't work?
Redirect hose from thermostat to the heater and run the return back to the water pump.
I 'll add shut offs to bypass the heater in the summer and run the coolant from the thermostat directly back to the water pump.
There is a problem with these as they go open after a very short time.
Maybe the water drops below the heater a little and they burn out.
You might want to check yours if it's older than two years.
Time for an oil immersion heater.