Maybe as an idea
get a popup slide in camper, lighter weight, less drag = better economy, all the comforts of home.
Using the appliances and other items from the lance in a sprinter van gets to be a big job maybe bigger than you might think.
Fabricating and installing a 6' slide seems like a can worms waiting to be opened, not saying it can't be done but its a lot of work. I could refer you to "covet the camper" on you tube, he is only repairing his slide, not starting from scratch, it looks like a big project.
taking in to account the work, expense, time, and money... and when your done you got a Sprinter