I use the definition of "how long until a trip by vehicle away from the site is necessary"? (Nothing is available). Mild temps.
In which case it's fresh water capacity that is the limiting factor, for general purposes. Propane is a very close second. Really, a camping RV isn't such without propane given its functions.
So, the only trick is to ascertain X-people versus Y-gallons/water for a time line.
I figure mine at two people. I know two weeks is easy in the above. For four, it would be tighter.
I have yet to do it, but I'd be more comfortable with supplies for four for up to a month. Moving water to the trailer is then the challenge.
To that end (and others implied by this thread) there are strategies and tips from those who camp the winter on BLM land, etc. Lots of good ideas in those threads.