Solar: To Ground the panels or NOT to ground the panels?

positive ground controller has the + in/out (including + load terminal) of the controller tied together internally and uses the neg for regulation. Positives all have the same potential.

vise versa

If you want to use the load terminals' timed feature with a positive ground controller that has the batt neg tied to chassis then you can not use the chassis with the load, you would need a neg return wire to the controller load terminal.