Engine Cooling - why not....

Hi,
did a lot of research and thinking about my engine cooling/cowling lately.
It's a conventional VW-Dub powered pusher. There's quite a lot of space
below the engine an very few on top. I want to do a tightly cowled engine
(only the heads and barrels enclosed, not the complete engine under
pressure). Yes - I know the 'traditional' method is feeding the air under
pressure on top and sucking out below. But in my case things would be much
easier (and streamlined) if I would feed the pressureized air from below and
let the hot stuff exit through the top cover of the cowling. It will be an
aluminun cowling, so heat is not such an issue. Any don'ts except an
oil-spilled windscreen in case of engine failure (even then all oil hoses,
cooler, pushrod tubes will be -outside- of the pressurized chamber). Your
suggestions/opinions are highly appreciated.
Happy New Year to All