Axis and Vegas 24.1 floorplans will indeed be manufactured on E-350 chassis for the time being according to rep I spoke with. Other floorplans, which are longer and heavier, will remain on E-450. He said once supply of E-350s runs out, they'll likely go back to E-450s.
For those who may prefer the E-350 this may be an opportunity. Those who only want the E-450 now need to avoid getting an E-350 unknowingly.
__________________
|