For me, it depends on the outside temp. Above 70; skivvies. Down to abt mid 40's; long sleeve flannel shirt and sweat pants. Down into the 30's, all of the above plus a head cover and fleece booties. I also have a 12 VDC electric blanket and a fleece sleeping bag liner available if needed.
I will add this: since getting my Heater Buddy and using a 20 pound tank, temps inside my camper remain in the low 60's regardless of outside conditions. So now, mostly skivvies and a long sleeve flannel shirt at most. After I do some overnights in Michigan and experience January and February nights, I'll revisit this post to see if its still accurate!
In support of "situational awareness" and "being prepared", particularly at night, I ALWAYS keep my Levis, shoes, and a jacket immediately available in case I have to respond to an "outside" issue in a hurry.
How do I sleep? Great, and Im really good at it . . . .