Back when we were younger, we transitioned from tents to sleeping in trucks and, especially, vans. This was nothing fancier than a mattress in the back of the vehicle. Cooking was outside on camp stoves, a bathroom nearby was required (or at least preferred), and showers were often heated (or not) by the sun. It saved us the trouble of setting up and taking down a tent and rain was less of an issue. (I don’t like setting up and taking down tents in the rain.) We usually travelled without reservations even in the summer, could sleep nearly anywhere (parking lot, rest area, National Forest Campground with small sites), and could (and did) stop pretty much anywhere we wanted along the way.
As much as we loved that life, adding a cat and large dog made a van way too small. Trips are much longer since we’re no longer limited to a week or three of vacation. And having an inside bathroom is just much nicer for most of us as we get older. We purchased a small, inexpensive fifth-wheel five years before I retired and enjoyed the comforts of a bathroom and kitchen on our vacation trips and learned what we would want in a retirement fifth-wheel.