Hi wry, yes thought about a sunroof also but I think they would let in the sun through the tinted Perspex and I think also they are recessed and water would sit on them............king cole.....that's a good idea also.never thought of that, maybe will look at rusco next week, could even put 2 or 3 of them in the roof

 

I know this may not be what you are looking for, but I have seen these on delivery vehicles in Dumaguete. Would suggest going to one of the multicab companie like Rusco, as they would know if these or similar are available.
Where you can buy a Genuine Flettner Ventilator