Can you point out the specific models of RVs that use T&G subfloors and conventional home floor structure?
I have never seen such setup in any RV I have been in so I highly doubt what you say is true..
Been in RVs from the 1960's and up and so far none of those were constructed like a conventional home floor with T&G.
The problems you state with sandwich floors is not 100% true in all cases. The problem stems from manufacturers reducing the thickness of the sub floor. I have a 1980's TT which has 1/2" thick plywood as a subfloor, but it is also glued (laminated) to the Styrofoam insulation below it and under the Stryofoam is as 1/4" plywood layer.
Modern RVs instead of using 1/2" plywood subfloor are using 1/4" or a bit thinner MDF or strand board to save weight and expense and that IS the real problem.
The only way you can avoid the thinnest subfloors is to make sure you are not choosing the "Lite" versions but then it now is heavier than what everyone wants to tow with can tow and not to mention far more expensive..
MDF and strandboard can no longer be avoided, the cost of real plywood will drive a lot of consumers away from the RVs..