Bill, there was a guy down here a few years back that placed his keyboard on top of a pair or 12 inch speakers and the entire rig sat on his R-10 rock and roller cart. He powered the rig with a 12-volt deep cycle marine battery connected through a 3000-watt inverter. His wife sang with him, as they slowly walked through the NH corridors, she kept the cart in motion, while he played the keyboard. He also had a Yamaha 12-string acoustic guitar with a spring loaded pickup that mounted in the guitar's opening. He had a powered mixer that everything plugged into, and on a single battery charge, he was able to get about 3 hours playing time. He charged 150 an hour and everyone seemed love it. Unfortunately, he had a fatal heart attack and passed away a few years later while on the job. So this may be another avenue of approach for you to explore.

Good luck on whatever you decide upon,

Gary