The circuitry won't allow you to run the furnace and heat pump simultaneously.
If you really want to implement this, you would need to disconnect the furnace wiring from the control board in the Penguin AC/Heatpump and connect it to its own thermostat. You will have to change the dip switch settings on the AC/Heatpump to reflect that a furnace is no longer connected. You would also need a
12V source for the secondary thermostat.
The way your system is now, it will switch from heat pump to furnace below 37 degrees.
Question: To run the heat pump you have to have shore power, so why not have a small electric space heater for supplemental heat?
Below freezing you use the furnace as the primary heat source because the furnace ducting is routed around your tanks and will keep them from freezing.
Stay warm!!