We toured the plant where Jayco builds their big Pinnacles and toyhaulers. I snapped some phone photos of the reinforcing on a Lippert frame for a big unit. I think it was for a TH. Maybe it will give people ideas on their own DIY strengthening.
By contrast, this what I saw when we toured the Crossroads factory this spring. The frame may have been for a slightly smaller fiver, but not much smaller if any.
Following shots are of a rear hitch receiver mounting at Crossroads. The hitch is rated for 3000/300.
Apparently I didn't photo a hitch mounting at Jayco.'
:S
Currently RV-less but not done yet.