You have to paint the tank a light reflective color: white or silver (NFPA 58). I don't know of any reason not to coat the entire tank with any kind of heavier product, but if you're worried about it just coat the front and bottom where it would be most likely to get chipped.
The spray on stuff I've tried is brittle - more of a fake Rhinoliner look than a tough coating. White Herculiner or Kiwi grip might do a better job.