I like to get the water heater going as soon as possible after arriving at our campsite. I want to ensure we have hot water for when I'm ready to take a shower.
The water heater can be used on either electric power or gas power. Generally, if you stay in a campground for less than a month, fees for all basic utilities are inclusive; in other words, sewer, water, and electric are all part of the daily or weekly fee. However, if you stay for a month or longer, electric is often a separate fee. Since I try to be frugal and get the most for my money -- and since we normally stay at a campground for less than a month -- I usually run my water heater off of electric power. This saves my propane, which costs about $20 for 5 gallons.
Our water heater is 6 gallons, which is a fairly standard size in the RV world. Donna and I stagger our showers a bit, and we often take "Navy" showers; in other words, we use the water sparingly. We have a button on our shower spout that allows us to turn the water on or off. Even when switched off in this manner, the water stays warm; on older systems, the water would lose its heat when switched off. This was the case in our previous trailer. So, we get in, soak ourselves, turn the water off, lather up, and then turn the water back on and rinse.
Occasionally, we will take longer showers, but only when we know we won't need hot water in the next few minutes and only when we are connected to a sewer system.
So, for us, our 6 gallon water heater provides sufficient hot water. Some RVers, especially those with larger families, will run their water heaters on both electric and gas at the same time to speed up the heating process. It is my understanding that gas heats more quickly than electricity.
But Donna and I have never had a problem, so we continue to run our water heater solely on electric power.
After connecting the trailer to city water, we will open up the faucets in the kitchen and bathroom to run the water for a short time to allow all air to escape from the lines. This allows the water heater to fill up with water. Only after the water heater has filled up do I turn on the water heater. I don't want to turn the water heater on when I have an empty water heater tank; that could cause an element to burn out.
On my Rockwood, there is a toggle switch in an outside compartment that I manually flip to turn on the water heater. From what I've read on forums, some people prefer to flip a breaker or remove a fuse from the breaker box located inside the trailer. I have no problem with flipping the switch outside. It is a part of my setup procedure now. In fact, I find flipping the toggle switch easier. My breaker box is located below the fridge, and lighting there is poor. To turn the water heater on and off this way, I'd have to get down on the floor with a flashlight. I'd rather step outside and flip a switch.
After flipping the switch, we normally have hot water in 30 minutes to an hour. We've never experienced a shortage of hot water. But again, we are rather conservative in our use.