Noise doubles about every 6C increase in temperature, consequently you need a lot more subs to reduce it. If you're handy, knock up a little alloy box big enough to house it and stick a Peltier cooler on the side. There are several designs around, but check out Gary Honis' website for a good read.
If you're going to use it solely for astro it might be worth considering fitting a cold finger and removing the IR filter. The possibilities are endless!
