lack of circulation in new enclosure

[bidden]

Just built a multi-level melamine enclosure with sliding glass front.
I did put a vent in the back but I am having a major problem with a lack of air circulating through the cage. Has anyone had this problem before or a possible solution??

A couple ideas I had was to first try adding another vent. and if that doesn't work maybe hooking up some sort of vent-duct to the back attached to a fan to force air out. any other ideas??

Thanks.