Upgrades
Cabin Heater
The optional cabin heaters have local switches to change modes from Heat/Off/Fan. If left in the Heat mode, high amperage will be drawn through the cabin heater contactor when the key switch is turned on, which is beyond its design limitations. The toggle switches can be accidentally switched very easily.
Consider adding switches to your control panel to operate the heaters, with an individual contactor used for each heater. The original design had a separate 12V power source to power the fan, but a small DC-DC converter can be used instead, which simplifies the wiring.