The original question/discussion was on trailer length. I wasn't aware of how important that was until I read this writeup published over a decade ago - I think physics hasn't changed since then, so this should still be applicable.
In there, the recomended safe trailer length is related mainly to TV wheelbase and the distance to the trailer hitch. Based on proper setup, there are tables giving maximum recomended lengths. There aren't many calculations and not much design data - but it is full of historical data; and that is more important than any prediction. He does point out that 5th Wheels are allowed 10% more length (due to hitch location). And he stated Hensley setup may allow a similar relaxation based on it's projected pivot point.
It is well organized and nicely written - very informative. And it takes the guess work out and gives us comfort ... or not depending on where you are.