I think the real value of an RV chassis may not be in a conventional one with living quarters, but in one that serves as a specialized facility on wheels. A mobile
dental clinic*,
health clinic,
veterinary clinic**, workshop/machine shop, soil testing laboratory***, or so forth is going to provide much greater functionality than a few cases of portable equipment. With proper staffing, it also becomes a serious resource that can be used to barter with survivor communities. In this scenario, the PCs can either be part of the primary specialist team, "convoy" security and scouts, or other support specialists.
If you want to stretch the concept, you also could build a convoy around a
mobile command post, which serves as both team comm/ops center and a link back to a higher echelon to which the PCs presumably report.
Going a little farther afield, I've always thought a racing team's support trailer would be interesting as a base vehicle (particularly in a Merc: 2000 setting). With one of the bigger 53' semi-trailers, you get living quarters
and a workshop area and tools. Fueling that prime mover is gonna suck, though.
- C.
* After three years of unchecked tooth decay, how much would you pay for anesthesia and professional removal?
** May sound useless, but consider its value in a livestock-dependent agricultural community.
*** Likewise a potentially priceless resource for re-establishing agriculture after several years of nuclear and chemical warfare, population movement, and uncontrolled industrial waste releases.