Hi Slydog, I have a swan ob on order and went through this with the dealer as the standard payload for all campers is 300kg. I have twin water tanks(among other options) getting fitted and pointed out to them than I can only load 140kg in with the tanks full. They gave me the 2000kg straight axle and have requested a payload upgrade to 375kg from jayco. Jayco have told the dealer they can upgrade the payload on most campers but depends on the weight of the van once it is built. If you get the 16in wheel option it reduces the braking capacity and limits the ATM to a lower value than the 15in wheels, although they wouldn't give me the exact details on this. The dealer also let slip that jayco have to fit the 2000kg on campers with twin water/gas tanks and don't charge the dealer extra for it, so don't pay extra you get it for free. Just make sure it is in writing on the order confirmation when you sign it.
Good luck and Happy camping Fryzy
