navegator's advice is spot on. A "B" can be cramped, and the bathroom isn't that big. Plus, "B"s are not cheap. Except for the Winnebago Travato, expect to pay near six digits for one... and even though a "B" has great MPG, the price difference can buy a lot of fuel.
If you downsize, you might look at a smaller "C", so you have the ability to get into smaller spaces. The Trend is an option, as well as the Phoenix Cruiser 2100, and Nexus RV's 24 footer is also viable.
I am sure you know this, but be wary of the MPG trap. Yes, a chassis might have twice the MPG, but the cost difference in upgrades will pay for a lot of fuel. The key is if you like the new motorhome for getting around in better and like being able be inside it for a rainy day or two.