Functionally you can use flat cable for UART type comminications over some reasonable number of feet. For longer distances consider the use of a simple foil shielded cable.

As a matter of fact your best bet, if going outside the equipment case is to configure the serial comms to use defacto standard D-9 style connectors. Then you can use off the shelf round type cables that can be purchased cheaply for lengths of 3 feet to over 100 feet.

Michael Karas