My Caravanner has 3 roof vents. Originally, all three were standard 14"x14" aluminum Hehr vents. They were in poor condition, with missing and seized cranks and dented and missing lids. The first photo shows a giant Tupperware lid being used as a temporary lid on one of them.
Between my two trailers and parts I've accumulated on eBay and elsewhere, I have plenty of good spare parts to make all 3 open and close almost like new again...the only problem was the old fans in them. Even if I could get those working, the old Hehr aluminum blade fans were just too noisy and inefficient.
I decided that I would like to have 2 of the 3 vents outfitted with modern powered fans. By far, the best powered fans on the market today are made by Fan-Tastic Vent. Recently, my company Vintage Trailer Supply started selling gray Fantastic units with gray flat lids. I worked with Fantastic to develop this special style unit specifically for vintage Airstreams. To demonstrate how great they look on vintage trailers, I put them in the rear two locations on my trailer.