I’d say, for a setup with 500 kcmil wires over 12 feet, a 6-inch tray should do the trick. I ran a similar setup once and found that going with ventilated or ladder-style trays helped keep things cooler since solid trays can trap a bit of heat with those higher-amp cables.
If you’re keeping things neat and out of sight, something like an
Under Desk Cable Tray is also handy, though it’s typically more for, you know, office setups. Just be sure to leave a little breathing room between the cables if you’re going the uncovered route—helps with airflow and keeps everything running smoothly.