I can certainly understand the appeal as a travel vehicle, where you carry your own minimal bathroom, cooking and sleeping space. The problem I have with them is that minimal side of things, with often minimal cargo capacity, small fresh and waste water tanks, etc. Using the specs from the Jayco, this is Promaster 20 ft chassis with a 9,350 GVWR, depending on floor plan you will have circa 25 gallon fresh water tank, with a 15 gal gray and 12 gallon black tank. Assume on average 1 gallon per toilet flush, and you get 6 toilet uses per person between needing to dump the black tank, On the gray water side, a typical RV shower flows about 2.5 gallons per minute, so your gray tank will allow for each of you to have a single 3 minute shower between emptying, of course by the time you combine those 2 numbers you will be out of fresh water. What this means is you will need to dump your waste tanks and refill your fresh water on a nearly daily basis with 2 people if fully living out of a class B. This of course can be extended if you limit your use of onboard facilities. Then of course there is the 6 gallon propane tank, which itself would be a similar limitation if camping in colder weather.
In my personal taste this is all just a bit too minimalist to see this as a living situation at my age, though I started out my own RV adventure when I was much younger with a couple of camper vans from the 1980's / 90's , what I can say about them is they were a BIG improvement over tent camping. Where I can see the appeal is mixing class B overnight stays with motels / full service campgrounds with shower facilities, etc. It all comes down to how you want to travel. The real advantage I see to such a small class B is that it is small enough to act as a nearly a daily driver car, that Promaster is a foot shorter than my crew cab F250, which I used as a daily driver for a number of years. By contrast as you get into bigger motorhomes, it becomes increasingly difficult to use them to get around, it is not just the increased length, but perhaps even more the increased height and width that limit where you can go (due to overhanging tree limbs etc).
By a point of contrast we currently have a 28 ft class A, which has 80 gallon fresh water, 40 gallon gray and 40 gallon black, along with a 32 gallon propane tank. Giving us enough tankage to go at least 3-4 days between dumping and refills without too active of water conservation efforts, and each of us taking a 2-3 minute quick wash shower each day. It also allows us to have a dry bath with a 32 inch neo angle shower and a queen size bed. Whenever I go look at these 20 ft class B's they always feel like they are about a quarter of the interior space as our 28 ft class A, the reality is this is a mix of them being a foot or so narrower, having less headroom, and about 8-10 ft lass interior length.
)
