Hello,
How about this to help dissippate the NP200 excess heat?

One could easily braze (either silver braze or silicon bronze) a pocket to the NP200, put two fittings in that pocket and route the return line from the heater to that pocket. That way, the heat would be absorbed by the engine coolant and dissippated by the radiator. Brazing is very easy and there would be no need for a separate pump or cooling circuit.

Any thoughts?
Mikel