Water Heater..

4 electric elements...then there is a problem with miswiring or high voltage condition

2 t-stats......either the wrong ones were installed (12V DC vs 120V AC). Your Suburban WH uses two different sets of t-stats ie: 120V AC set for electric element and a 12V DC set for the propane.
OR
Improper installation......not tight against a clean area on tank wall, forcing the connections on bending terminals which loosen them up or high voltage conditions

I have an '07 Montana with the Surburban water heater and have never had a problem. I always use both the electric and propane.
And I frequent the Montana Owners Club forum and water heater problems is not something that comes up very often. Certainly not one failing as often as yours.

Ours did the same thing. I ended up installing a Hot Rod & haven't had any problems since

Is you water heater plugged into an outlet or is hard wired into a junction box?
I would verify that the system is properly wired. It may have the neutral and ground reversed.

No, it's never on when tank is empty. We camp all summer and the water heater isn't emptied till winterizing. It is a Suburban. Had four heating elements and two thermostats, so far. Works fine on propane. My mechanic suggested just using it on propane, but that does not sit well with me, since it is a two way heater.
My mechanic is the one who suggested this problem is caused by the heater getting too hot. Seems the t stat should stop that from happening. Also had it repaired by the dealer. They know less than the mechanic. This is the 2012.

What water heater do you have.
Does it work properly on propane?
It is not "common" as I have had several rigs with no real issues.
If this is on the 2012, I would say installtion or product problem.

Just in case... It's never switched on when the tank is empty, is it?

I know it would be very easy to forget to turn it off when we plug it in at home.

Common problems with elements are build up on the element form lack of draining/flushing tank, turning element on without water in tank and loose/bad wiring at terminals on element.

Common problems with t-stats are loose/bad connections on terminals and lack of proper tank wall contact.

What Brand/model?
What do you mean 'gets too hot'?
How many elements have you had to replace?
How many t-stats have you had to replace?

Mechanic says, "It's common."
Not common with any of the water heaters in any of the 4 rigs we have owned...

4 times in one year and he can't find the problem?
Next step is a different mechanic.
Good luck with it.