Hi and welcome.
That water heater uses a 12V DC circuit to run the igniter for the gas, but it draws little power. The manual only specifies 18GA wire for that, so it's just a few amps at most.
The 1400W element is a 120V AC heating element, for when you're plugged into shore power.
Those are separate circuits so the heater will work on gas (with 12VDC) or electric (with 120VAC).
Here's the manual for it:
https://highskyrvparts.com/downloads...n%20Manual.pdf