Every year we've mounted ours on a piece of plywood. Simple, cheap, effective. This year we're using some ESD-safe plastic-like material (not really sure what it is, to be honest, but it is ESD safe), because we could pick it up for free from one of our sponsors. Then for most runs on the robot itself, we use some slotted plastic wire duct (
http://www.mcmaster.com/#wire-duct/=5j2cg7). Of course, if you have wires that run onto moving parts, you have to make allowances... but using this stuff we can ensure that shorting to the frame is only going to happen under exceedingly exceptional circumstances.