I have the identical vent as well. I also noticed some deterioration around the plywood flooring in this area, whereas the rest of the floor in my Caravel
is solid. I have been tempted to cut out the marginal wood and re-build the vent somewhat smaller, but haven't because I've assumed Airstream knew something when they designed the hole so big!
Stef, I have a home-made looking windblock as well, made of galvanized (?) metal. Perhaps it wasn't homemade after all?