Thermo-King APU and Espar Heater

[Possmguts]

How would you set an Espar Heater to stay on with the key in On?

Was able to figure out how to keep the APU running with key On but not the Espar.

Kind of a pain to want to roll down a window and have the heater shut off because the key had to be turned On to do so... Or while waiting on the truck to warm up it would be nice to keep the Espar running too...

I would rather manually shut the APU and Heater off myself than them shutting down just because the key got turned on.