You essentially need a smaller version of your main tank. I use a 40 gallon tank, with MH lighting, skimmer, etc. It's set up bare bottom with good flow provided by the return pump and a few power heads. The key is observing the corals for trouble signs and taking appropriate measure if needed. I keep all new SPS corals in QT for at least 8 weeks.
You can probably get by with a 10 or 20 gallon with a h.o.t skimmer...