Don't think the t/stat controls the gas,only the heaters
Try the 230v and 12 volt heaters to refrigerate.
Some 12v heaters will only come on when engine is running,you should feel heat coming up from the round insulated cylinder, (very hot top pipe) if not the heater elements may be faulty.
If heaters are OK, sometimes fairly violent shaking side to side of whole fridge (do not turn upside down) will clear a blockage in refrigerant system
Norman
January 2009