My wife has Crohn's disease which is a big reason we are buying an RV...so a 4.6-gallon "cassette" tank isn't going to cut it for our needs. Both the bathroom size and the tank size are high on our priority list. We know all class b bathrooms are tiny...but some are still way bigger than others. The Solis's is super tiny and has the smallest capacity. Too bad, because otherwise we rather liked it.
You are likely set on a class B, however, a small class C could give you much larger tank. https://www.rvingknowhow.com/typica...wheels usually have the,from 27 to 63 gallons.

