Hot water Heater not working on Electric

Many Mobile Home and RV connections use "displacement" aka "piercing" or "punch down" connectors. Both Junctions and Receptacles, probably also Switches, can be wired using these. Clearest example is this Scotch Lock type where two wires lie parallel in the housing and then the little metal piece is squeezed down, cutting through the insulation and wedging onto the conductors. EDIT: THIS CONNECTOR IS PICTURED AS AN EXAMPLE OF WHAT NOT TO USE BECAUSE THEY FAIL!!!
Our RV had ONE OF THOSE junction boxes on the floor inside a cabinet connecting wiring from the breaker panel to a short pigtail coming back from the water heater. The Neutral (White Wire) side had arced and became an Open. I'd heard of this before on water heater circuits. I took the connecting metal pieces out, gutted the plastic to form a Box, stripped and mechanically twisted the wires together. I then screwed Wire Nuts over the connections, taped them against unscrewing, and "punched" the cover back on. Fine since.
Note: the splice where a flexible shore tie cable splices to the hard wire used within an RV often fails and has to be re-done. Running resistive electric heaters seems to contribute to that.

Your Atwood model uses one set of t-stat/eco, one control board and same DC Voltage for heating with electric and/or propane.

The 120V AC to electric element is triggered via a DC Relay

White wire to circuit board is the DC from electric on/off switch
Then DC must go to/thru t-stat and back to circuit board
Then a very small millivolt goes to/thru ECO and gas valve so ECO is part of control circuit

THEN DC goes to relay to trigger AC to element
Any loss of DC prior to relay will not allow electric element to function

AC at the DC relay and element can be issue also....there are on backside of tank under the black protective cover......PITA to access
SO check DC circuit first

Here is the wiring scheme

First step would be to take the electrical cover off where the wires connect to the water heater and see if there is power there. Ensure you have positive power on the black lead when measuring it to the ground lead, and that you have power from the black to the neutral.

Next is shut off the breaker, remove the wires from the heater connection, and measure the ohms resistance across the heater element. It should be well less than one ohm, more like 1/10 of an ohm. If it is more than that, it is broken inside.

I haven't looked at many... not sure if they have a plug in connection like the fridge does. If that is the case, try with a good extension cord before anything, then do the tests.