I have never understood that number.
For example, we just stayed at a Florida SP a couple weeks ago. Reserve America lists the site we are in with a 40Ft limit.
I was actually thinking about this very question that you posed, and I stepped it off. Now I can't remember the number, but it was ballpark 80ft that could have gone in that spot.
A few weeks prior at a different SP, the 30ft limit site we were in could fit around a 40ft rig.
The 80ft and 40ft numbers I mention would be TV + TT OR MH
I think the published limit is supposed to be the "camping unit".... the TT or the MH, not including your TV but based on my experience the "camping unit could be a lot more usually, with the TV parked beside the TT or perpendicular to the space.....
