How cold is too cold?

  Yes.  You are likely to have problems.  The pod's water tanks and some of the lines are exposed under the trailer.  They are close to the ground but up in the air.  They cool off fast.  My lines started freezing at around 25 degrees at around 12:30 or 1am.  I'm sure they would have burst by morning if I hadn't turned up the interior heat to about 95, opened the panels to the inside plumbing and, since I was alone in the campground (well after normal generator hours), I turned the exhaust of the generator to blow warm air under the pod.  (This did set off the CO alarm rather quickly.)  I got by, but barely, and only with a lot of effort.

  I was at Yellowstone just about exactly a year ago and I'm pretty sure it got into the teens.  At that elevation nights get cold fast.  I'd plan on dry camping.

  See my reply yesterday to the post on camping in North Carolina for more on this subject.

  TT

Just got home from Yellowstone and had a great time.  Low temp was 23.7 degrees, measured on a picnic table bench at our site at Grant Village.  I did not have any problems with the pump or lines freezing.  Saw lots of wildlife, and not too crowded.  Wonderful time to visit.  Leaves were changing in Grand Teton and all the way home.