So, since it on a permanent site, when was the last time the unit had the anode removed and the unit flushed out?
CLOSE the winterization valves and TURN OFF the outside rocker switch
Remove and inspect the anode while draining the unit from the outside of the rig.
Replace anode with a new one if needed (betting you will).
Flush from the outside with a flushing wand that will fit into the anode hole.
Water Heater Tank Rinser - Camco 11691 - Water Heaters - Camping World
Tape the threads of the new anode with Teflon tape and replace it
Open the valves to "use"
Make sure your pressure relief valve opens and reseals as the water heater fills.
Turn on the electric element.
I am pretty sure your tank is loaded with sediment.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW