All Airstreams and almost all RV's are "three season" insulation. It's intended for use when there is not a lot of snow on the ground. It's not just insulation, there are also issues with things like plumbing and other odd things.
More details: you have about 2" of fiberglass in the walls. You also have aluminum ribs that go directly from the outer skin to the inner skin. On top of that, the windows are single pane designs. You have some air space under the trailer between the pan and the floor. There often is not a lot of insulation there. Floor loss is generally not the biggest deal anyway.
Heating (or cooling) wise, maintaining a signifiant delta between indoors and outdoors will take a lot of power. The same "30 degrees or so" that applies to cooling in the summer also is pretty close for heating in the winter. You may get the trailer to 70F when it's 100F outdoors under "best case" conditions. Getting it to 70F with 30F outdoors is a bit more do-able, but not by a lot. You can supplement either the heating or cooling with added devices. That's going to up the energy bill pretty fast.