Sue urban 6 gal water heater

I change the anode twice a year routinely and a new one installed as I replaced the heat element.

When is the last time you changed the anode? If you have mineral buildup that is the first thing you need to deal with.
As old Bi posted the 120 volt side is very simple. Power in, switch, hi limit switch pack, element. The off/on switch is a known weak spot. As is sharp edges that eventually cut wires. Without a volt meter your kind of stuck throwing parts at it.

Suburban Water Heater AC power is a simple circuit

*120V AC from Main AC Power Panel circuit breaker (turn off then back on to make sure it wasn't tripped)
*120V AC Power goes to AC Junction Box on right side of WH Tank (looking from inside RV at backside of WH. (Wires connected with wire nuts....check that they are actually connected/tight)
*120V AC then goes to the ON/OFF switch (in outside compartment...lower left corner)
*120V AC from switch to the AC set of t-stats....black wire to top t-stat (Hi temp...manual reset/trips at 170*F)
*Then down the fused metal wire to bottom t-stat. Normal temp t-stat/Opens at 130*F (check that the fuse wire is intact)
*120VAC then goes to the electric element (black wire) and then returns to AC Power Panel (Neutral/white wire)

Green wire to secure/clean grounding screw connection



Suspects...
AC Junction Box wire nuts
Fused wire between Hi and Normal t-stats