The lightest is the one with no options, no water, minimal batteries and minimal propane with minimal personal belongings in either truck or camper. :)
Seriously though, I think lightest would be a Host or Eagle Cap with the entire list including a Lance, too. I don't think the difference in weight will be that significant unless you have a full tank. The Host in some years has more water capacity ... I think.
My Host double slide with all options is stickered 3571 dry. It also has 60 gallon water capacity. On my SRW, I never carried that much water and even having a nearly full black or grey tank was noticeable. With my F450, I'm not careful about what I carry.
