You could easily mount the fans on the back of the canopy. If at all possible you want the cooling fan blowing the length of your reflectors and having as much air passing across your ballast ass possible. Exhaust fan is'nt as crucial (especially if you put a couple of vents on top of the canopy, heat rises
) Also make sure you put spacers between your reflector and canopy. This allows more air cirrculation around the reflector and bulb for heat dispersion.
Heres an idea. Mount your reflectors/bulbs running the length of the tank. Put a couple of vents on the top of the canopy. An exhaust fan on the backside of the canopy on one end. With an intake fan on the other end. Now lets get creative. For the intake air you could build a shroud of some sort to dirrect air across the length of the reflectors/bulbs (make sure you mount your ballast to where they recieve maximum air flow from the intake, either on the back of the canopy or perhaps lined up between your reflectors).
In example. Lets say you have a 2" dia. intake fan. You could easily buy some 2" flexible hose and bend/fasten it to where air flow runs the length of the bulbs and across the ballast. The exhaust on the other end would help pull the heat out from under the canopy and away from the tank.
As you mentioned, with this many ballast as well as other heat sources (
PC, electronics, house lighting, mother nature, etc) in a small room, heat dispersion is going to be a PITA. A 10 hour light cycle might be a good idea. Hope your not sleeping in this room this summer
Just an idea......
HTH