When you get your Lance 855S, be sure you get the AGM batteries, not the wet cells you have to check and fill, It's just too hard to do the maintenance on them and to ensure they are vented correctly. Verify the hand operated crank for the slide out works. Just in case... Check all the water fittings. We had the outdoor shower fitting only finger tight and it leaked, showing up on the outside near the shower and bath. Check and make sure the emergency disconnect switch works correctly too. If the dealer is wiring up your truck with the proprietary plug Lance uses, make sure they do it per the Lance manual with the ground and the hot lead 8gauge wire directly to the battery via a breaker. You should get both propane tanks filled when delivered too. Our dealer gave us something like $150 credit at their RV store where we bought a water pressure regulator, an upgraded sewer hose and the rest towards the Lance shock struts. BTW, those struts, while expensive, make all the difference in the world on providing a smooth ride. I can't say enough good things about them. Our dealer also said we would get 15% off anything we bought through them, like the struts. I used the Torklift tiedowns and really appreciate how strong those things are.
Hope you enjoy your camper as much as we do ours!