Buying a "NEW" motor home on a year old chassis means that the chassis has sat outside, unprotected, for a year. The tires have aged a year. The engine may not have been run for a year. The belts and hoses have aged a year. The chassis has probably started to rust and depending on whether or not the storage was in a field, various critters may have started nibbling on the wiring. I do not know of any RV manufacturer that stored unused Chassis inside their warehouse away from the elements.
But other than that, if the RV house is put on a year later, some salesman may be able to convince you that you just paid a lot of money for a "NEW" RV.