Underseat heaters starting in 1937 & 1938

Does anyone driving a 37 or 38 Chrysler have the optional heater under the front passenger seat?

I have a C17 Airflow with one. Apparently in 37 or 38 it started as an option for Chryslers, but I cannot find documentation about them being in the 37 Airflows. Looks like this could have been a late option for the C17s. There's an extra button and extra thermostat on the dashboard, and heater hoses feeding through the floorboard, and I'm trying to understand the configuration. If anyone has one, do you also have an extra (100 - 212) thermometer? Any information that could be provided will be of great help.