The only test equipment I carry on the road is a 12v
test light and a cheap voltage indicator that plugs into a 120v outlet. I guess I have one of those 3-light 120v outlet testers in the shore power locker but I don't think I've ever used it.
The running, stop, tail, and turn lights, and the electric brakes, are the most important items and are the most likely to fail. A test light is the best way to troubleshoot those sorts of problems.
I've had my eye on this tester which I think would be ideal for RV work, covering both AC and DC systems:
GTC CM100 1 mA to 100 Amps AC/DC Low Current Clamp Meter : Amazon.com : Automotive