We have a dual gas / 240V 14L in the van. It only uses 850W on 240V. Enough for both of us as wife showers in morning & I shower just before I got to bed. Use it more on gas as free camping never includes 240V. And when we do have 240V, I tend to use the shower in the van park.
After many moons of having no hot water with my Girrard continuous flow hot water heater I bit the bullet and spent the $$$ in September 2017 and had the Suburban you are thinking of fitting, fitted. Best thing since sliced bread. Hot water when I want it now.
I was only going gas but after a chat with the people doing the job for me and only a few extra $$ I decided on gas/240v. I am so glad I did too. Saves my gas if on 240v for any reason.
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Live Life On Your Terms
DOUGChief One Feather (Losing feathers with age)
TUG.......2014 Holden LT Colorado Twin Cab Ute with Canopy
DEN....... 2014 "Chief" Arrow CV (with some changes)