FWIW, here's how I handled a similar problem. This is in my aluminum truckbox and I installed a temp-controlled fan both for cooling and airflow. I used an oven thermometer to test it and make sure the temps stabilized. I bought aluminum roof vents and riveted them to the ends of the box. The sides and top of the box are lined with
B-Quiet Ultimate material to deaden the sound. This stuff is (supposedly) safe for temps up to 300 degrees. I tested it at various distances with a decibel meter, but I can't find that spreadsheet anymore. It was pretty quiet, and my wife described the noise as "about the same as the dishwasher" when it was running. We used it in Yellowstone (no-gen area) and no one noticed during the day.
I realize this isn't exactly your application, but might be good for some ideas...
The metal hose is to carry away the hot exhaust (so it doesn't concentrate on one spot in the box wall).
Obviously, I have to empty the box before using it, but can store stuff in the open area while traveling.
Here's what it looks like closed (this was in my old truck). The gaps on the sides were plenty large enough for the airflow, and it has the added advantage of not being obvious to thieves (that a generator is there).
