There was an example of this at Purley on Thames. In the 1920s or 1930s a field near Mapledurham Lock was acquired at auction by a speculator who divided into plots and sold it for cheap holiday homes - mostly old railway carriages, caravans, huts and similar. Many were bought by Londoners, who then moved into them permanently, especially after the Blitz began. The "Purley Park River Estate" came into being.
After the 1960s a process of gentrification, encouraged by the local planners began and helped by the fact that many of the residents were getting old. Plots were consolidated and redeveloped and most of the badly rutted gravel roads made up to highway standards and taken over by the highway authority.
One of the converted carriages was rescued and is now at Didcot - see
https://didcotrailwaycentre.org.uk/article.php/145/no-2511-dean-6-wheel-family-saloon