The cab is in a closet? Do you keep the closet door shut? Where is your intake air coming from? Where's your exhaust going to? The closet? You can intake from the same room you exhaust to (I do), but if you do then you have to keep that room temperature-controlled, else heat builds up, and if your intake is bringing in heated air...you will have probs. You should probably get the cab out of the closet either way, as that is probably contributing to heat buildup. Easy way to test that - just move the cab out of the closet to a cool room and run the light for four hours, then check the temps.

If that's not the problem, then you'll need to get a beefier fan. I'd think a 4" centrifugal fan (Eco Plus, Vortex, whatever) would be the best solution. You could try the fart fans and such too, they might work. And get a homemade or purchased cooltube for your light too. If you can't afford a centrifugal fan, then a squirrel cage fan is the next best option, followed by fart fans and axial fans or whatever you can scrounge up.

The good news is: dealing with heat inside a cabinet is the biggest problem you're likely to have. Once you solve this problem, things will get a lot rosier.