I just picked up an used Arctic Fox travel trailer that has a Fantastic Fan knock-off in one of the crank up roof vents. First trip out was about a 45 minute drive down one of the dustiest roads I’ve ever driven on, before I started on the dirt road I closed all vents and windows except the vent with the fan. I turned the fan on mid speed with the air blowing into the trailer and when I arrived at the campsite there was zero dust anywhere inside the camper.
I wasn’t convinced it was just the fan keeping the dust out so on the way back down the same road I did the same with all the vents and windows but didn’t turn the fan on.
Good god, when I reached the end of the road it looked like I had just driven across the desert, I couldn’t believe how dusty it was inside. Now I admit I forgot to close the vent over the fan so it may have been a bit better but going forward, anytime a dusty road is involved, the fan will be running.