I had to look up stainless braid wiring to see what you were talking about.
A couple of problems that I could see......
#1) any inspection of the trailer with wiring NOT inside a wall that can be exposed to being handled or snared by humans could be a big no-no by a DOT inspector.
wiring is different than 120v, 12v
is strand wire and 120v is solid core wire. The reason stranded wire is used for 12v
systems is to increase contact at connections and devices to reduce voltage drop. I'm just not sure if you could get stainless braided wire in the necessary gauge thickness that you would require, (12 volt wire for lights needs to be very thick).
#3) Weight; how much will that stainless wiring weigh?
IMHO I would still run wiring inside the walls, but by all means protect the heck out of it. I have used plastic tubes vulcumed into place in ribs for running wire and try to minimize how much movement the wiring will move.