Ha, and last night I was researching on electric wheel chairs in order to modify one. I want to build something similar to Sea Legs Rib, but with my smaller Zodiac, although not nearly as cool, and electric power. The problem is the wheelchairs are not designed to handle salt water so it can only be used "near" the water. The search for a cheap/free chair begins. Then I will build front launching wheels that pull the boat around, as the rears need to be used underwater for launching and recovery. I already have another set of Wheeleez sand tires for the front.
I have seen a few different styles of trailer movers. For one of my friends we bolted a winch to the floor of his garage in order to carefully and slowly pull his boat in. The winch had a wireless remote so it could actually be accomplished with one person. Pulling it out from the garage was usually much more involved since once the front wheel left the garage it wanted to head downhill, so again the winch was used to control the trailer.
Pigs, as they are referred to for airplanes are most often gas powered, and can move fairly heavy objects around. Today an electric unit would probably be preferable for convenience and noise. For light weight trailers and short distances a power drill setup works. As shown in the video a cordless would work, but the only one I have seen in person was a 1/2" corded drill that had a decent amount of power and was permanently fixed to the Pig. Longer and you will need a real motor. The more gear reduction the more it can pull. With a welder everything can be built fairly easily once the parts are sourced.