Ford has a toll free number dedicated to motorhome assistance. If you need service they will find a dealer who will help you.
The number is in the Owner's Guide in the glovebox.
As for warranty work, what warranty work? Hopefully your Ford will be like our 2010 E450. The only thing that has been done on ours is front end alignment. We've not had one trip to the Ford dealer for warranty work. Not even a light bulb has failed.
Speaking of front end alignment, chances are yours will need it. The Ford chassis seems to settle in and the alignment changes. The previous Forest River rep who participated in this forum said it's best to get about 3000 miles on it before alignment. After that they don't change. So pay attention to how it drives. If it pulls left or right, tell your RV dealer who will get approval from Forest River to pay for it. Since they "completed" the vehicle, they are responsible for that part of it, not Ford. Just so I don't leave you confused, almost all other chassis related parts are under the Ford warranty.
2011 Sunseeker 3100
1997 Pathfinder Toad