funny you should post this up because thats what i'm kinda thinking of doing the same thing as the BMC CDA my mate has will be fairly tight in the space at the top of the engine bay as its a larger capacity one (150mm wide and 200mm long).
However... I'm still a bit apprehensive about a setup like that. Although its all closed off (BMC system or the Blue filter cover pic) and you will be ducting air from the fog bezel, water or crud doesn't have to travel very far before hitting the filter element. (when you think about it most cars have the filtering happening above where any crap can reach.) Just something to consider.
Its gonna be good to see everyones systems in awhile
: :1syellow1