The AmpTraXX is intended for vehicle applications, and we really have no precedence for it being used in a rack. Be sure it is well ventilated with nothing on the top of the unit otherwise it may overheat.
Regarding the power input, simply follow the specifications included in the User Manual. It will need 18-24VDC at 22Amps (max).
The power cable is supplied. One end has a Molex connector that plugs into the unit, the other end is bare wires.