In the hot summer months, I leave the overhead vents open and a couple windows cracked open, one in the front of the TT and one in the rear.
Aero-Flo Vent Covers.
In the winter months, I leave the overhead vents open slightly, all windows closed and a small thermostatic controled electric heater "ON" in the center of the TT.
The TT is always under cover
in my back yard, so I don't worry too much about the weather.
Since June the TT had been plugged in to shore power with the A/C & Fridge running, when we're not out camping.