Those are nice vents, Chef; but, once ya add the cowl it ends up well past $300 per unit!!
I have a defunct solar fan/vent in the head. While the dorades you linked would look/work nicely; spending one-tenth the price of my boat for a funnel would be a tad nutz.
I'm pretty good with sheet metal and have some s.s. around the shop. A few hours making up a box and mounting some sort of cowl will eat up some of the winter blues.