I did not see this addressed previously, but please appreciate the fact that your most likely scenario is to unhook your towed vehicle before you enter small parks for some obvious reasons.
In that configuration, you only need to wiggle your 40 plus feet between the trees and can backup and re-position far more easily. It it not realistic (to me, anyway) to limit yourself to pull throughs, and many parks like Corps of Engineer parks often have a picture of the actual site. Google maps satellite views are helpful, but there's not substitute for personal inspection, that not being always possible.
Again, as mentioned, tight roads, branches, and turning radiuses are often more key than actual site depth.
We are currently in a Corps park, with narrow roads, lots of trees, tight turning radiuses, and angles less than 45 degrees. However, our worst issue was soft ground such that we were in mudholes if we could not stay on the pavement. A man has to know his limitations.
Over time, lots of researching, talking to park rangers (not always reliable - "oh, yeah, sure you can get in there..."), and getting recommendations is your best bet. Your parking skills will improve over time, so use a little extra room until you are really comfortable in a small space with a big piece of gear.
The key to parking in small spaces is good on the ground direction. I hand direct Christi everywhere we go and she is extremely skilled. Not trading paint with inanimate objects is the skill you want to master.
You can do this!
Kim