Electric hot water on fifth wheel .

Depends on how many times it cycles during the evening.
Water is heated to 130*F. Heating will turn back on when temp reaches 100*F

Electric heating is roughly 6.2 gallons per hour but that is based on cold water replacing the hot water not just reheating of water 30*F


Savings over a month would only be a small amount.
One that shouldn't make a budget difference.

How much is electric .......kw/h cost?

We pay $0.15 per kw/h here in AZ

Check your usage for a couple days leaving it on, then check a couple days turning it off. Then you'll know for sure.

No one on here can tell you with any degree of accuracy since there are lots of variables. Maybe you have lots of mineral build-up in your tank, maybe your insulation is crushed in spots, maybe your heating element is going south, etc. Check it and find out for sure.

The water heater has a thermostat in it. It is efficiently turning itself off and on for you so you don't have to.
The heater is not on all night the thermostat is turning it on and off.
Turning it off in the evening and allowing the water too cool off will produce negligible savings.

As quickly as our units reheat, you will probably save a little each cycle. It will not be enough to finance a new truck, but it might pay for some adult anti-freeze.