You could leave the ballast outside the canopy would that make for more room?
I'd recommend a set of 24" HO T5 retrofits like what J&L sells too because they are much more efficient than PC lights. Two T5 bulbs would be more intense light output than 4 PC bulbs.
You could cool your case with little VGA or "chipset" fans from a computer store like NCIX. Cut the "blowholes" in your canopy with a hole saw and use fan grills to keep it tidy. Power it with a 12V 1A power adapter from the source or canadian tire.
http://www.ncix.com/products/index.p...%20Corporation
This will give you lots of light output and will deal with the cooling of the canopy quite well.
Or maybe consider a new tank and canopy? That might be the easiest and best solution?