You are correct, DPeakMD, the electronic ignition Atwood requires only 12 V DC to be hooked up to it. Atwood supplies a nice switch for the ignition and the instructions are pretty clear and straightforward.
In our rear bath model, I just used the DC circuit that went to the small exhaust fan in the water heater closet (which I had removed).
The supplies required to install the water heater include some 16 ga wire (forget Lowes and HD and go to NAPA), some wire nuts or butt connectors, screws, and caulk or butyl tape.
On the 6 gallon Atwood we installed, the gas connection was sufficiently different from the old Bowen that I had to run a new supply line. That required a flaring tool, copper tubing, and teflon tape (the yellow color). Since I could not budge the old valve, I replaced it as well.
Atwoods are built for rectangular SOB's, so you need to decide whether to shim up the bottom of the heater or live with a variable thickness caulk joint on the outside of the trailer. At least there was enough inward taper on the side of our '74 to require that choice. Different years/models may have straighter sides at the water heater.
I would not say it's a very difficult job to put one in, but it will take some time and patience. Good luck either way.