Welcome to airforums.com, Sargon. I hope you enjoy your visit to our planet.
Good luck with the financial plant to own an Airstream; these days, we often need to adopt unconventional plans to achieve our goals.
On a slab in a shed, you shouldn't have much of a cold winter problem, despite the average and even peak lows in St Peters. I would still skirt the lower section of your trailer, and then even just a couple of 100 watt bulbs left on constantly should prevent freezing of the plumbing, I would expect.
You have an exceptional resource here in the accumulated knowledge on this board, so don't hesitate to ask questions.