I like wolfe10's suggestion, but I would try to find a parking lot with some lines on it. Line up the truck/trailer on a line, and then do a 180 and see where you land.
If you get a numberlet's say 50', then I would use 75'. I have no clue if my numbers are even close to any reality.
Note the difference between turning radius and turning diameter. We often use the turn turning radius, but what is off quoted is turning diameter.
Let us know what you find: My wife and I have often talked about moving out to the country, and I have wondered about what I would need to pull of the maneuver you are contemplating.
2020 Chevy Silverado 1500
Forest River Wildwood XLite 263BHXL