I think you'll regret your decision very quickly. Many good points were made regarding the difference between sharing a plane and sharing a motor home. A couple more that come to mind are damage to the RV. If you nick an aircraft wing, it will have to be immediately serviced and repaired by a certified technician. A motor home will often be damaged, small dents, backing incidents and often a decision is made not to repair due to cost and difficulty. They can accumulate and later devalue the RV.
The other issue is time sharing. Typically you fly a plane over a one or two day period and return. With an RV, it's often taken out for one to two weeks or more and usually over the warmest part of the year, limiting the time both owners get to use it.