Yep, azdryheat has it right. I have two on the 3800 that vent the attic space. Incidently, one of them holes never was drilled all the way through, I poked it with my finger and the plug fell through. The other one, the plug is still in place until such time I get back up there and drill it out.
One more fine operation by the visually impaired that build our RVs.
I thought the Cyclone vent was mainly for motor homes that have people inside while rolling down the road. Living full time in the 5er for almost a year I still haven't found a reason to add them, maybe someday but not yet.
2013 Voltage 3800, 2012 Chevy 3500 HD
2010 Yamaha V Star 950
2009 Yamaha Raider
Volunteering with Habitat for Humanity Caravanners