It is much easier to adapt interior cabinets and components to the square fiberglass “box” of a class A, C or B+ than to the unusual curved shape of the Roadtrek’s interior. In addition, it is more difficult to get all the equipment to fit comfortably within the limited space of a Roadtrek—and, when off-the-shelf items are not suitable, it’s often more expensive to get custom made or modified components such as water tanks and propane tanks.