So Im wiring my amp into my 05 Dodge Grand Caravan. The spot Im going to be placing my amp is in the stow and go behind the front passenger side seat.

NOw the Stow and go compartment is pretty much a metal shell with carpet on it, but the outside edge had a plastic runner with metal bolts going through to attach it. This is the location I was thinking about grounding the ground wire. My only concern is its a plastic hole with the metal bolt through it with a metal nut, would this be a suitable place ?

 

No sir not a good spot. Any chance of plastic being between the ground lug and a solid metal connection from top and bottom (nut/bolt on top and metal on bottom) is a bad idea.

What I would do is run the ground wire under the carpet towards that door sill (remove the plastic runner first) and towards the front. At the bottom corner of the front door right there should be a footing for the front seat seat-belt. I would try to get the ground to that point and screw down as close to where that seat-belt screws down as I could. Reason being where that seat-belt bolt is anchored is a nice thick piece of metal that should give you a good ground point.