We have a 220" wheelbase and I'm kinda with DrewE that you might be overthinking it. It will take some getting used to and some back and forth depending on the site, but we can fit quite a few places. Many take more than one maneuver, but who cares. For us, coming from a truck and TT it is a million times easier backing our C.
The cones idea is a decent one, but I feel like real experience is best...or put a cone where you a tree might be (where you don't think it is humanly possible to maneuver in there!) I also think that cones aren't going to give you enough height for a visual in the front and in the mirrors. Maybe with poles and flags???
But honestly, forget that there might be people watching and snickering and take your time and do your thing :)