Suburban water heater.......
6 gallon electric/gas will fit same opening as the old 6 gallon gas only.
If you are looking at 10 gallon you will have to increase opening in side of your RV.
Electric......
Uses 120V AC directly from AC Dist Panel so you would need a Circuit Breaker for it. Wiring would need to go to AC Junction box on side of WH tank (Hot/Neutral) then you just connect to WH OEM wiring.

Propane......
Uses same propane line and same 12V DC wiring (IF Current WH is DSI Spark Electrode). Just need to connect existing wiring from ON/OFF switch to DC Junction box on side of WH Tank (OEM Wiring)
Otherwise you may need to run new DC wiring

What model of Suburban?
Pilot
Pilot with re-ignitor
DSI (electronic spark electrode)
Making it work properly could be cheap.....what does it do/what does it not do??