I just put "trailer mover" into Google and found walk-behind dollies priced from about $30 to over $5000. Can't pick out one for you, since I don't know your budget, how much trailer you need to move, and on what surface. The $5000 mover would probably work on any surface not too soft for the trailer tires, many of the others have skinny hard tires for use on hard surfaces.
Local RV dealer uses a forklift with ball and fiver hitches. Jayco factory uses small farm tractors, lifting with the three-point.