A Disappointing Surprise with the Water Heater

Re the NEC, yes, some of it's there to prevent people from sticking their tongues on a frozen lamp post.

To use an over used cliché, at the end of the day, the users manual should adequately explain the switching systems for the hot water heater and it doesn't.  Strictly speaking, the rocker switch on the water heater and the breaker should be enough, but only if they were well explained and the user was advised that the electric and gas functions are as different as a ......[I was going to put in some names of political parties, but out of respect for our very wise no politics policy] ....fish and a house cat.

The breaker is, as Mike and I agree, a "switch" in the technical sense.  It is designated, as I previously noted, SWP so it can be used repeatedly as would any regular switch.  [Though in a very technical sense it violates the NEC, but that's the least of our worries.]  The problem is with using breakers for switching the water heater off and on is that: 1, most people are not accustomed to using breakers as of and on switches; 2, the breaker is not necessarily labeled; 3, its in an awkward location where it is easy to accidentally flip if you happen to be turning off or on other breakers; 4, there is a switch for the gas system inside the trailer in a convenient location and many are confused about it's function [i.e. the dealer who told me it operated all the hot water heating functions - kind of like "Automatic" mode on some refrigerators that selects gas, battery or AC.]; 5, the cost of putting a switch -- that  yes is redundant -- in a convenient spot is minimal and would be much more understandable to the ordinary user.  

So, yes, such a switch is triple redundant, but so is the thermostatic switch for my furnace in the house.  There is no reason [except the NEC orientation requirement] that I couldn't go out in the snow to turn off and on my furnace or boiler [actually boilers have a required 3rd redundant switch usually painted red] instead of operating it from the convenience of my nice warm hallway thermostat and off/on switch there (more redundancy) or going into my garage or basement to turn it off an on there at the furnace.

Yes, from a technical person's point of view the redundancy is overkill, but from the lay person's point of view, or what we call in my biz the "ordinary and reasonable user," a clearly marked easy to find and operate, and inexpensive to install, switch may be more sensible. Ford Motor company learned this the hard way in order to save $15.40.