The RV Consumer Group can be a valuable resource, I have used them every time we have bought a rig.
No they don't "buy" every rig, no they don't even walk into an example of every model offered.
They tour factories to look at construction methods, they look, in detail, at an example from every model line, they do have "formulas", but these formulas are based in common sense, like the ratio between total length and wheel-base. As noted above, a longer wheel-base (for the same total length) is safer then shorter. Yes it will not handle well in "in town" driving, but honestly, were are you using the rig?
Another thing they look at is were tanks are located. Well, located, centered, balanced gets a higher "score" then a builder that puts all the tanks on one side, or towards the back (better balance, better handling)