Just as a datapoint ... we (myself, the DW, and a small dog) have a 24 foot Itasca (Winnebago) Class C motorhome with no slides and have taken several long trips in it lasting up to 10 weeks and at a maximum travel distance of around 9000 miles. We do not tow a vehicle ... we can use the relatively small motorhome for all errands and sight-seeing side trips. No problems living in the motorhome for those many weeks and miles. We were not burned out at the end of the trips.
For a certain kind of people, smallness of the RV is what is wanted ... kindof like living in a cosy cocoon that it is easy to keep warm, easy to keep cool, easy to park, and easy to drive. We're not necessarily outside folks. We mix it up with some outside exploring (short hikes with photo taking or hunting for rocks (in good weather), some outside sitting around a propane fire eating or talking or reading (weather permitting), and some inside reading or movie watching (in the evenings and during bad/cold/hot weather).
It should be very possible to full time in a small RV - as long as one's health remains fairly good.
