As part of my annual water heater service, I decided to upgrade our propane-only unit to dual function by adding a electric heating element. I chose the Hott Rod HR-6 universal kit for 6 gallon tanks, and added the PSK1 Hott Rod switch kit for convenience. The installation is fairly simple, and can be accomplished with a few hand tools. The photos below show the steps.
With heater off and cold, remove the drain plug and drain tank. Flush out sediment. Install adapter bushing in the drain hole, then add the heating element. Attach the electric power cord. This was where I hit my first snag. On our Atwood heater, the propane supply line runs close by the drain plug. I was able to install the heating element without any problem, but the electric plug, which has to snap on the end of the element, was a VERY tight fit. By trimming the rubber lip on the plug, I was just able to "persuade" it into proper position. Any tighter and it would not have worked.
Drill a 1/2" hole through the heater front plate sheet metal, then feed the power wire through the hole. Put the split flex loom stuff on the wire to protect it. Next, find a spot to mount the thermostat control. This is the 2nd place where I had a small difficulty. The thermostat has to stick to the metal water tank, and on our coach, access to the tank is VERY limited. I finally decided to try a spot just behind the steel beam that supports the water heater. I cut the cardboard tank cover with a box cutter and made a flap, which I then peeled back. The fiberglass insulation stuck to the flap, exposing the metal tank. Used steel wool and alcohol swab to clean up the mounting place.
Before mounting the thermostat, you need to set the desired temperature, hook up the power wire, and (if you are going to use one) connect the switch. I set the temp on 140 degrees (no kids) to help extend showers. The wiring harnesses supplied in the kits are very good quality, and go together easily. You only need to crimp one connector (if you use the switch). Connect the wires to the thermostat, and then peel the paper off the double sided tape, and stick the thermostat to the tank. The instructions say to let it "cure" 24 hours, so I folded the flap back over the thermostat and held it all tightly in place with a stick of wood. Quit for the day.
Next morning, all I had to do was mount the switch and tidy up the wiring. Electrical power was easy, because I already have a extension cord in our water pump bay (for Winter heater). I thought about trying to put the switch somewhere inside the coach, but after looking at how difficult it would be, decided to pussy out and mount the switch in the heater bay. I figure we will only use the electric heat when we are plugged into shore power - otherwise we'll use propane. It won't be any problem popping open the bay door and flicking the switch on after we park and get the coach hooked up.
I mounted the switch on the support beam under the water heater. Collected all the wires and tired them up out of sight behind the water heater. Filled the water heater with water (VERY IMPORTANT), then plugged the heater cord in and turned on the switch. The switch lights up when the power is on. I could hear the element come on and start to burble, so I knew it was working. Went inside, had some dinner. Came out about 45 minutes later, and checked hot water temp at the bathroom faucet with digital meat thermometer: 140 degrees EXACTLY!
I think this will be a very nice addition to our coach. It is quiet, and it will save on the use of propane when we have full hook-ups. If we need hot water REALLY fast, we could use both the propane and the electric element. Several reports I read online said this combo will heat water almost as fast as you use it, and can extend showers almost indefinitely. Can't wait to try it out! 
Amazon.com: Diamond Group (HR6) Universal Hott Rod - 6 Gallon Capacity:...
Amazon.com: Diamond Group PSK1 Hott Rod Power Switch Wiring Kit: Automotive
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Topic: Hott Rod Installation, Atwood GH6-7E