how do you prevent the reverse flow during the night when the cabin is heated? Do you cover a inlet? Other wise the heater is doing the exact opposite by pull in the heated air and cooling it.
There is a method one can utilize that involves building something similar to a trap on a drain line the prevents back draft. I incorporated on my solar heater, works great and is maintenance free. No opening or closing or blocking inlets/exhaust.
I dont know if my sketch makes sense. I can explain it better if interested.
Whats better then a screen is a curved surface. If you look in the drywall area at a home improvement store, you will see a rounded corner bead made out of thin steel. Those are incredible for collectors. My lil secret.