[BB_TX]

Are you reading the 110...115 directly across the element terminals? With good solid wiring connections, I would not expect any appreciable voltage drop thru the circuit. I suppose there could be some small drop across some of the contact points, but I do not think there should be 7-12 volts.

I am assuming the 122 volts is at a random outlet inside the trailer.

I would use a long piece of wire connected directly to my neutral bus bar as a solid reference neutral for my volt meter. Then, using that reference, I would check the voltage at the load side of the water heater circuit breaker in your distribution center, both terminals of the thermostat, and at the hot terminal of the element. And both sides of the switch, if feasible. You should have that 122 volts at the breaker. If not, then the breaker may be flaky. The other points should all be at or very near the same voltage you measure at the breaker. If it is not at or near the 122, then there may be loose/bad wiring connections in the hot side of the wiring to the element, including the switch and thermostat connections.

And then measure the voltage at the neutral side of the element. That should measure at or very near zero volts. If it is measuring several volts at the neutral side of the element, then there may be a loose/bad wiring connection on the neutral side causing that voltage drop.

This could explain the lower voltage. But I am not sure that would explain the lower temperature.