yo! , yes you need a box
not only will this seperate the cold air from the hot air which the pod would be sucking if purely exposed under the bonnet, if you get pulled over u will get a canary due to the pod but if its in a box it should be sweet.
there is a template floating around the forums i think INASNTS name comes to mind...do a search on these forums and im sure you will find the template...making it up would be a piece of piss.