Pull out or push in the knob on the fan that rotates to open the lid. This disables the lid open or closed. The fan will still cycle on/off but the lid will stay open. To answer your question, no I dont know what replaces the wall thermostat. We do as above with a max air cover on the fantastic vent to keep rain out. You can call Fantastic Fan (someone will post their number). They have great aftersale support and can send you updated parts for your model to modernize it.
Robert & Nancy with "Murphy the EOG"
Murphy has passed on, but Micah and Bogie have assumed the watch! 02 Holiday Rambler 5ver, 2015 Indian Chief Vintage. 98 Coachmen truck camper.