their campgrounds or there campgrounds? I don't know where there is...
Is a carhauler special? You are talking about just a big cargo trailer I assume? Because the carhauler that the big semis tow with two levels and ramps and are open would not be something you would want to use as a base for an RV build.
Cargo campers, on the other hand, are quite common. very common. You would do better to try a non-google search and just type in "cargo camper" and you will find thousands of pictures or articles or whatever fancies there your desire for more info.
Self-built RVs are common, much more durable and give the owner just what he wants, here or there, but I do not know about the connection to any campgrounds.