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Class B RVs are built in a van platform. In the past they were built on passenger van chassis (right) but Eurovan chassis have become more common as their market share increases.
Class B motorhomes present several design challenges that make the cost surprisingly high. First, the RV amenities are built within the existing chassis and skin, which limits access for workers and fitment.1) Second, the available space is much smaller than on class A or class C.
The payoff is a more durable, leakproof motorhome with higher build quality.