MH ballast location

[awilds]

Hello all,
I'm in the process of putting together a new 120 gallon reef tank. Just
got the lights last night (2x250 MH + 2x110 VHO). Mounting the lights
in the canopy should be no problem.

My question is on the dual ballast that came with my retro kit. This
thing is huge and I'm somewhat concerned about the heat it will
generate. My orginal plan was to mount the ballast to the back of the
base cabinet. There is not enough room inside the cabinet (because of
the sump) and the heating would probably be even worse there.

So, I'm thinking I should place the ballast maybe inside, or on top of,
a seperate smaller cabinet that will sit next the tank. This would keep
any heat well away from the back of the tank or the sump cabinet. If I
set the ballast on top of the cabinet, it may not look the best but at
least air could circulate around it.

Any other ideas are welcome. This is my first setup with MH. My
existing 55 gal tank has VHOs so never really had to deal with a heat
problem there.

Alan