I drilled a whole in the firewall on the passenger side.That is how I ran most of my power wires for the last 12 years.Just easier then trying to find a spot that is useable.However if there is one(rubber graumet) and will work with the wire I am running then I'll use that.As for the ground I use one of the rear seat bolts that I cleaned up as the ground.I am still debateing on using this for this application or if I should run a full ground wire.
If you look at one of the pics you can see where I am talking about.It is the piece of black wire wire I attached the strapping to.