Just Google camper van rentals and you should find lots in Europe, England and Germany especially. Lots of places to stop, on the mainland you can stop for the night almost anywhere with no hassles, including highway rest areas, shopping center parking lots, and much more. A little more restricted in England, but we got a guide "Pubstops" with listings of Pubs that allow you to stay the night. In fact we found a great Christmas dinner through "Pubstops".
Remember that fuel is much more expensive in Europe and a medium size or larger (higher than 2 meters) camper will put you into class 2 on the toll roads. The combination makes travel in some countries a bit dear, although one can always avoid the toll roads.
A totally non-sailing related picture of a tormented gargoyle on the Salisbury Cathedral