solar deck vents for cars

[ben]

Hyatt (1990 200TQA) is getting old, but that gives me the opportunity
to play with her, right?  Here's what I'm thinking:

Most marine hardware stores offer solar-powered deck ventilation
fans.  The idea is that you drill a hole in your deck and put one of
these in, and get fresh air all day.  Sounds like just the thing for a
car in Colorado, doesn't it?

For example, here's one:
http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&classNum=12407&subdeptNum=12406&storeNum=12&productId=13726

1) Has any of you done anything like this?

2) Any advice for drilling the 4" hole in my roof?

3) I'm assuming that air is free to come in through the normal
   ventilation system if I didn't turn it off.  Or do the vacuum
   control lines have to have vacuum to open it?

4) It can be opened from below, and since it's meant for boats that
   might take green water over the deck, I suspect that "100%
   waterproof" is good enough for cars.  But do you know how
   waterproof they are when open?  Good enough for thunderstorms,
   hopefully?

Cheers!
-Ben

-- 
Ben Pearre          1990 200TQA          http://hebb.mit.edu/~ben