We made the trip last summer in our then Lance Cab-Over-Camper. No problem with ULSD. In fact no problems at all with anything. Only thing was my wife and I got a little claustrophobic in our 11' 3" camper. Get the latest addition of the Milepost. That's a must. It tells you where you can get gasoline, diesel and ULSD. It tells you whats available in every little town along the way and it includes the latest maps. I started a thread that has about 172 posts called, "Alaska Trip in a Cab-Over-Camper". It has much needed information. Do a search by Grizzly on Towing and Hauling and RV Forum, page 13. I started it on 21 Feb 06 and the last post was made on 14Jun 07. There are also many other threads on Alaska. You will love the trip, just give yourself plenty of time. Feel free to ask me any questions.