I like the idea of generating a strong charge while moving. Lots of trucks have 240 to 300 amp heavy duty alternators rated for this kind of charging. Thanks to the need from the ambulance market and crazy loud car stereo market you can get kits for up to 4 high output alternators!
As DKB said, you will need a huge dedicated run of heavy gauge wire from the alternator to a special connection between the vehicle and trailer to get more than a few amps even at highway speeds.
I also like the idea of free power from solar and wind, but I ain't staying too long anywhere the wind is blowing that hard.
Dual Alternator Kit, Triple Alternator Kit, Quad Alternator Kit, GM-Ford-Dodge-Nissan