There are basically two kinds of RV’s (Recreational Vehicles): trailers, which are pulled by a car or a truck, and motorhomes.
There are also two kinds of trailers: travel trailers, which are connected by a hitch at the rear end of the tow car/truck (like the ubiquitous European Wohnwagen or Caravan), and fifth wheel trailers, which front ends are shaped like a gooseneck and are connected to a pickup truck with a hitch that sits inside the truck bed.
Like always, both concepts have their advantages and disadvantages. Travel trailers don’t need a truck to be pulled, just a normal car or SUV. And they are available in very small sizes, with the so-called pop-up campers being the least expensive way of RV-ing. Their problem: the longer they are, the more unstable is the car-trailer combination, subject to the dangerous jack-knifing in high cross winds or upon breaking under slick road conditions. This is why most people who want long trailers, say above 30 feet, prefer fifth wheel trailers. They are available up to 45 feet, absolutely stable on the road and very easy to drive, despite the length. That’s also the reason why virtually all full size commercial trailer-trucks have the same fifth wheel hitch principle. Disadvantage: they need a dedicated towing vehicle, which makes the whole thing much less affordable than a travel trailer.
Basically, there are two categories of motorhomes as well, called Class A and Class C (there is also a Class B, but that’s less than 1% of all motorhomes). Class A’s are built like buses, on their own chassis, and usually pretty big (30 – 45 ft) and expensive ($80,000 – over a million). More economic are the C Classes which have the RV built on a pickup truck as one unit. Most of them come in sizes of 20 – 30 ft. Virtually all commercial rental RV’s are C Classes, because they are relatively inexpensive and easy to drive.
Modern trailers and motorhomes are often equipped with so-called slide-outs, meaning that a part of the interior can be moved out of the main RV body when stationary. That increases the living space considerably which could be 400 sq ft and more in larger units (36 qm).