Haven't seen much of anything like that since the '60s. There was a time when you could build along the Intracoastal Waterway or backwaters, but even then you had to build, not put a trailer on it. Changes in the law since then have further limited development along public waterways and on reservoirs, and most of your "lakes" will be, like ours on the Plains, reservoirs.
I think you can still find property like that in places where they have thousands of little lakes (in the Northeast would probably be called ponds). Northern Minnesota, southern Michigan maybe. I still see trailers and occasional RVs on the lakefronts there.