what kind of ballast is it? electronic or coil?
What type of lighting is it for? halides, PC, VHO, T5?
Generally, I would say that your ballasts need to be placed as close as possible to the bulbs without causing any concerns or saftey issues. A lot of people remote mounte ballasts in the stand, others on the back of the canopy. Personally, my ballast is mounted inside my canopy, but it is a waterproof casing, electronic VHO ballast. It gets hot, but not to the point where I cant touch it.
Ballasts will get hot no matter what. Electronic ballasts wont be as hot as coil ballasts though. Not much that can really be done about it unfortunately.