Which Dometic?
Are the panel lights ON?
Are you running it on GAS.........15A shore power is marginal due to other AC power demands
IS RV LEVEL.......can cause damage to fridge cooling unit if not level when operating it.
Takes several hours for fridge to cool down.....freezer section FIRST then food compartment.
Water heater.
Look in outside compartment for Brand & Model....info on sticker
Cold water inlet valve. It is a 3 way valve.
With handle pointed same direction as cold water line then water should flow into water heater.
With handle turned 1/4 turn and pointed in same direction as bypass line (line that connects cold water inlet with hot water outlet piping) then water flow is around (bypasses) water heater. In bypass cold water will flow thru/out hot water but not into water heater (check valve in hot out stops backflow into WH Tank when bypassed)
With water supply on..pop open Relief Valve (outside compartment) and check that water flows out.
No water......heater bypassed.....don't turn on water heater w/o water in it!!!!
By turning electric ON you have most likely burnt out the element.
Element NEEDS water to cool it otherwise it burns out
And trying to run everything on 15A shore power will NOT work
Not enough AMPS being supplied