They made the switch in the last part of 2015 by which time they were calling the units the 2016 models. I purchased my "2016" Vegas 24.1 at the end of May 2015 and it was on the E350. The more recent "2016's" are coming out on the E450.
Sheree & Michael NCNG LTC(ret) with Munpi and Sheba (cat).
2016 Vegas 24.1 E350 5 speed "Ms. Enterprise", Bug-Guard Screen, Recliners, Infotainment Center, HUD, ARC Shower Rod, Safe-T-Plus, Curt SpareTire Mount,Tornado Black Tank Rinser, ext. WiFi Antenna, Roadmaster Tow Sys& Invisibrake.