If the front end is out of alignment and you don't have hefty Anti-sway bars, the motorhome will wander. Our 32' Jayco Greyhawk handles great and has since the day we bought it new and drove it 800 miles home a few weeks shy of 6 years ago. It came with aftermarket Anti-sway bars (I want to say Hellwig, but I'd have to confirm that) and Hellwig helper springs on the leaf spring pack.
The manufacturer should do an alignment after they build the house on the chassis. If they don't, with the added weight, the alignment can be off. Make sure when you test drive, the dealer lets you take it on the highway.
I would expect Winnebago to align their Motorhomes after they build the house.
-Michael