Brand and model help....!!
Suburban SW12DEM
That is a 12gal combo with electronic ignition AND motor aid (engine coolant runs thru a 'U' tube on back of WH tank....heats water while in transit)....so you should have Hot water upon arrival.
The 120V AC is 'direct' (NO DC USED/REQUIRED).....AC circuit breaker to ON/OFF switch (outside compartment lower left corner and MAYBE an addition one inside RV---if RV Mfg. installed one)
Outside On/Off switch corrodes due to exposure.....always first suspect.
Next is the 120V AC set of t-stats (under rubber cover---Push to Reset-----left set with black wires*****right side 12V DC propane red wire)
High temp trips if normal one fails....manual reset (normal/130*F--High/170*F)
Connecting wire between high and normal burns sometimes burns thru
If high temp tripped then normal t-stat is bad....replace set
Then there is the element.....
120V AC (black wire) to element ---thru element ---returns to AC panel common (white wire)
Should measure 10 ohms resistance.