Did it many years ago in my old TT which wasn't the best insulated. Low temps were in the 20's and I used enough gas to keep the interior about 50-55. Worked fine for me.
My last trip in my new 5er, which is far better insulated, saw lows of about 40 and once again, I kept the interior about 55 or so. I wouldn't hesitate to go into the 20's or possibly even lower. I also have a heated belly for the tanks, R38 insulation, I'm perfectly happy in a cold room sitting under a blanket, etc.
It depends on the unit, how prepared it is, and how cold we're talking, but in general you should be fine. Keep an eye on your LP levels as you can go through that pretty quickly.
Now-2014 Sierra 346RETS 5er BUB
Then-2002 Keystone Springdale 286RLDS TT
Nights camped in 2014-28, 2015-127, 2016-10