The logic defies me. If living in a poptop is acceptable and has more room then just pull it with a car. If towing anything with a B then why not a small car? Some can be easier to tow than a poptop and a car is certainly easier to use for driving around than a B. Plus with two RV units you have way too much redundancy. Then again, towing anything is a severe limitation to owning a B and its advantages of going anywhere in the first place. If towing then owning a much larger RV towing a car or a car towing a hard shell trailer makes a heck of a lot more sense for extended stays.
Two other things. First, you already think a B is too cramped. Maybe it isn't for you.
Secondly, towing a poptop is not going to get you in small campgrounds. If a campground is limited to say 24 feet as a lot of National Forest campgrounds are, you have no room for a Class B and a poptop. As Handbasket mentioned too. One camping unit per site is a norm and if allowed then an additional fee.