There's a couple things you can do to remove the heat factor from that closet:

1) Remove the ballast to a box outside the closet........helps quite a bit.
2) Add another cooling fan directed towards the bulb.......usually with my set up the oscillating fan I use for the plants hits the lights but I also have a larger area to work with than you do.
3) Your best bet is to probably drop the bulb wattage down to a 400 or 600 and put the 1000 in a drawer. The higher wattage the more heat.......your ballast will still work with a lower wattage lamp and with the use of Mylar you can still get the desired effects your looking for with that small of an area.]

Have a good grow!:thumbsup: