I have this stuff called heatshrink that is like a sleeve that you cover the cables with and then heat it up with a heat gun. The sleeve/tube shrinks and huggs the cable like a glove its also waterproof and stops anything making contact. You cant get this stuff from your auto store its used in electrical industrial applications for high voltage powercable. I havnt fitted it to my Ute yet because the engine bay is being painted at the moment. But you can get it in Red/White/Blue and Black. the datsun colors what more could you want.
And i will be running the Battery in the Tray too.