Steep turns in the dark? Sitting at my desk here I felt as if i just dropped 300ft just reading that!
Ah, forgot to add a little power to your desk, and pitch your chair up a bit, surely?
Seriously though, the only significant difference between steep turns in the dark and steep turns in daytime is the lack of a good horizon, so you've got to determine bank angle from the AH instead of by looking outside. But even in daylight you will need the altimeter to determine whether you're losing height or not. No different in the dark.
The things you need to be more careful about are stalls. When you don't have a visible horizon, perform a fully developed stall and mismanage it, you might end up in a spin. Not good.
And if you do PFLs at night, well, realistically it's not going to accomplish much with regards to training. For safety reasons you've got stay above MSA or be absolutely sure there's no unlit tower or something in your path. And since you can't see hedges, barbed wire, ditches and so forth in the dark (unless there's a good moon), where are you going to go? But that question needs answering regardless of whether it's a practice FL or a for-real FL in the dark.