Yep he does reference NEC which has nothing to do whatsoever to do with a Mobile Radio Installation. NEC is for building and home wiring. Not applicable, out of scope, and has no other purpose being there other than taking up space to fill a page sounding important. There are some parts of NEC you can get some guidance on most notably is roughly what is the smallest wire you can get away with used with what size fuse. But here is the catch, yes it is safe, but may not work well. Reason is simple, NEC is not a design or How-To document. It is minimum life and safety requirements and does not address performance issues like voltage loss in low voltage systems like 12 volts. If that 12 AWG with a 20 amp fuse, 18 amps when in TX, with say 20-feet of 1-way wire distance is going to loose about 10% voltage and power. One thing the NEC or Marine electrical codes would never allow you to do is use Ground (chassis) as a circuit conductor like the Automobile industry. That would be extremely dangerous and a lot of people would be hurt with fatalities, and property damage.