Few things... you would also need a few switches as well, to swap between propane and electric options. You would need both of these for safety. Dont want your water heater on if its empty. You would also need to run 12VDC and 110VAC to this heater. DC voltage runs the control and ignition system.. AC tuns the.. well.. AC element. Electrical load on the AC and DC side would increase as well. Much like your leak detector, it would pull constant battery power for the system, both on propane, and AC voltage.
The new heater would come with a wiring diagram. Your original looks like its an Atwood G6A-6, Gas Only, Pilot Ignition (Jayco PN 0017371). Direct replacement is an Atwood, but no model listed, Direct Spark.. NO AC ELECTRIC element (Jayco PN 0178155).. (2012 model).. Atwood upgrade SHOULD work. You may have to get a bit creative on wiring.