Greetings stormdeborah! Welcome to Air Forums. Your post says Trade Wind. I have a 66 Trade Wind, so I thought I'd take a look.
I believe Fantastic Fan and Maxx Fan sell 14" square units that would replace the roof vents in your Trade Wind. Check out Vintage Trailer Supply. They can be ordered with translucent plastic "hats" so you can get light into your trailer. I have never seen a plastic vent cover that would "rivet" onto the existing herr helix lifts our trailers were made with.
I might add that the plastic translucent vent covers on our 86 Airstream sun baked brittle, and then cracked up in a hail storm. Plastic doesn't have the life of aluminum.
I hope you enjoy exploring the Air Forums and learning all about your Trade Wind as well as helping others with things you have learned. You'll have to post a picture or two of your rig. It's fun to see other Trade Winds.