There are two major types of RV's - motorized and non-motorized. The only non-motorized RV's one can consider as a full timer is the the fifth wheel or fiver and the towable trailer. Both of these require heavy duty trucks to tow them so both of these are not a consideration for us if we were to full time in an RV.
Motorized RV'S are generally the preferred choice of many full timers in the USA. They weigh from 15,000 to 35,000 pounds and can be as long as 40 plus feet in length. The biggest are the Class A units which have all the comforts you would expect in a "stick" home without the grass to mow. They are usually on a 3-10 ton truck chassis and will typically have many slideouts. Class A motorhomes range in price from $100,000 to $500,000 an d can be even much higher.
Class B motorhomes or van conversions are the smallest RV's. Constructed on a van chassis they generally weigh less than 8,000 pounds and are usually less than 19 feet in length. These are generally considered too small for full timing in.
Class C homes are kind of like mini-class A's since they are simply scaled-down versions of them. They weigh from 10,000 to 13,000 pounds and are from 20 feet to 31 feet long. These are mostly on a larger van chassis which explains why the driver area is like that of a van. Class C motorhomes range in price from $50,000 to around $150,000.
Class A motorhomes are too expensive and too large for us. Class B's are too small. We really don't want to have to buy a huge truck so that really only leaves us with a Class C. This will call for further research!