Because most of the year I'm mainly touring (which means that I'm most likely at a FHU site), a "B" that gets more MPG than my daily driver and can slide into virtually any parking place is important, not to mention storage of the rig consists of parking in the driveway, and plugging in a cord to keep the batteries topped off.
Since I boondock in the same place for a part of the year, I might as well haul an enclosed cargo trailer that I can move to the campsite and leave there, partially as a place for additional storage, and partially as a way to show that a place is taken. Once the enclosed cargo trailer is in place, I only have one relatively small vehicle to worry about.
Plus, this gives me the ability to slap a solar panel or two on a trailer, which will more than offset the battery loss from the furnace without needing to fire up a generator.
Of course, the downside of the trailer is that one has to find a place to put it before being able to visit a town square, which partially defeats the purpose of a "B", but some items like motorcycles require it.
If I needed more room, I'd also consider a high quality hitch mounted cargo carrier, but even that can turn a "B" into something fairly difficult to park in most places unless one is able to take up two spaces lengthwise, especially if it is a longer Sprinter chassis.