If you run a dedicated 12 gauge (or lower) Romex (etc.) to your rig, and
use a plastic box, then you already have an " Isolated dedicated
ground." You only need an IG if you don’t have a dedicated run.
Sort of. Technically the dedicated run will be grounded back at the panel, which in turn is grounded to the service ground. Service ground is the copper rod driven into the ground, typically right beside the house and very near the meter.
Which you probably know.
The OP and all his comments are so infernally confusing even I was just about totally lost. The link he provides is just as bad, not one word on the page saying what exactly they mean by IGR. Had to follow a link to another page where finally it says:
IGRs are bonded directly to the service entrance grounding system.
So there you go. The OP had an electrician install an outlet with a ground wire running all the way back to service ground.