RV life looks fun from the outside. And a lot of it is. But the first year can feel like a crash course in everything you didn’t know. I thought I was ready. I had the checklists. I did the research.

Retirees Kay and Steve Parish have taken downsizing to the extreme. Earlier this year, they sold their 1,575-square-foot house and moved full-time into an Airstream trailer one-eighth that size. They ...