I've seen one parent at a local junior tournment using the tow hitch reciever on his SUV to string rackets. He was using a crank, though.
I would say your best bet is Alpha Revo 4000, Eagnas Combo 810, or a Gamma X-ST, all crank machines but can easily adapt a Wise. As for power, you can always use a small portable generator. I've seen a couple of stringers use a small 1000w Honda generator, or use an inverter for you SUV.
What kind of DW do you have now?
Machines: Gamma 6004 2-point w/ Wise 2086 & Babolat Sensor Dual