Just wanted to pass along some info to help out any other newbie Chateau 31L owners.
I found the 3 insect screens for the 31L for the water heater, furnace and fridge vents.
Water Heater is Camco 42145 Flying Insect Screen - Model WH 500
Furnace is Camco 42144 Flying Insect Screen - FUR 500
Fridge is Camco 42148 Flying Insect Screen - RS 500
Amazon links are:
Amazon.com: Camco 42148 Flying Insect Screen - RS 500: Automotive
2016 Thor Chateau 31L