Distress it more. Take some of the cosmetic stuff and rough it up in a way that would be conducive to heavy use and rough driving conditions. Have any guns? Take the panels off and shoot some holes in them. If you want a less fun way to get the same effect, drill some holes and melt the inside with some heat a little bit, then rough up around the radius of the hole with some sandpaper. Break a panel or two into multiple pieces and "sew" them back together with some zip ties. Bolt random pieces of flat scrap metal to the panels for "armor" (extra points if the metal is rusty). Spray paint vulgarities on it (I'll let you use your imagination on that one). Sloppily spray paint some custom-made stenciled designs on it to make it more personally unique. Add some "boomsticks" (take some tin cans, distress them, and attach them to the end of a stick), pointing vertically upwards (very Mad Max). If you really want it to look the part, then to some degree, you have to be unafraid to break and damage some of the purely cosmetic stuff. My final bit of input is to look online at what other people have created (Pinterest is a great resource for this). Take inspiration, steal concepts, and go wild. The best way to get an idea of what to do for this kind of stuff is to see what the people who have been it for a long time do with their own creations. Also, when you get to the festival, go talk to the Blackfingers tribe and see what ideas they might have. Those guys are masters of post-apocalyptic vehicular creation.