How about leaving it off for a month and just turning it on for 1 day a month ?.

Would this be enough to keep it functional and keep garbage from growing in it ?. If I shut off power should I shut the inlet valve ?

I had a farmhouse and drained the electric hot water tank every Dec. and filled it every April, it lasted 14 years with no heat in the house or power.

Thats alot of tanks...do you have a spa tub in mb?
One sug. is to "twin" the tanks (i.e. the output of one goes in the input of the other)
This way you can shut the heat source of one or more tanks off and still have the water flow.
Youll want to leave the last one in line on.

i had a water leak that was coming from under my foudation and i turn my heat water tank off to protect the elements in the heater until i got the leak fix in a few months then my heater was working afterward but the water start getting cold within a few minutes so my husband replaced both 2 elements and replace the breaker now there is no hot water.