Picture posting is enabled for all :)
Can you contrive a vent design that opens the flap down into the tunnel so that you are not putting up a "sail" that might put large forces onto the structure at a point where the least strength can be provided, or perhaps a rotary device that opens in response to the movement of the autovent arm. The lower "in vent " is a good idea, perhaps a roller blind device linked to a autovent arm?
Vinlander, So captured rainwater is your counterweight, a small leaking drum on a string, job done. Trickles away to allow return to open when sunshine returns. Just a case of caliberation . 10% royalties ok?, when you hit the market.