i dont know if anyone has posted this, but there is lots of empty space between the frame and the body, maybe you can retrofit some "steel plating" inside of the body, just enough to fit on the frame, and place some shaped armored plating anywhere it may make the vehicle look armored and cool...
also may i suggest using angled armor! most tanks have sloped armor, the "tomb stone." as they called it in death race was basically a 6 inch steel plate that sat on the back of the car, i was surprised they didn't make it angled to increase its effishency! for example, a peace of armored plate 3 inches thick, set at a 45 degree angle will hold back hits just as well as a peace of steel 6 inches thick set at a 90 degree angle! also i think placing angled armor in some places would really add effects to the look of the vehicle!