I like the tinned marine wire I get from the ebay source above. Its not the cheapest but is double insulated if more than one wire bunched. I started using it long time ago and everything has held up great from engine bay to interior. It also pretty flexible which is a plus.
We had a pretty good discussion when I did my original install on the matter http://www.risingsun4x4club.org/foru...ght=12v+outlet