I sent out a few emails to people who should have the experience with different brands (a repair guy and inspector). I had also asked around for a list of methods to consider, thinking surely others had to develop something like a spreadsheet to gather the data and then make their own decision.
Hope to find a starting point to compare against. I'd thought about breaking down the construction methods of what I might consider a unit built with no concern for price, using those methods to compare against. Keeping in mind price is not always an indication of quality.
You have brought up some finer points which about require a guy to study the actual materials used, step by step, for any one method - if that makes sense.
We have not decided between a 5th wheel or class a, much less diesel vs. gas. I can see making that decision might also help reduce the need to study every method of construction. Although I suspect some methods are not unique to either class of rig.