Hello;If you're gonna run iy under the car,I personally would use *Flexible Electrical Conduit*. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif .Some of it is steel reinforced w/ a duable insulation coating on the outside.I also would use a waterproof threaded grommet similar to the one StreetWire makes to make the entrance into the trunk area.As far as securing the cable under the car,I would also use steel insulated clamps and "Bolts,Lock Nuts,flat washers and Silicone",not self~tapping screws or sheet metal screws,which could loosen over time:vibrations and what not.Loom is ok,IMOO,I like something that is "Totally Encased" and more durable,"cause you never know about the extremes Mother Nature throws at us.
If you do use the Flex Slit Loom,just be sure to put the slit on the bottom so as water and such has a chance to run out of the loom //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif .Not Flamming on the other posters,just My views on what I would do //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif .All the Best with your project.Take Care.