Hi Pete,
I feel your pain. I too have a few failed inverters in my past.
Most of the time if not all of the time, there is a reason when mosfets perish. Usually the failure happens because of one of two things. 1... Load current exceeds specification in some way.
Load current sometimes just happens as part of life. Short circuit... like in my case, relay contact failure.
Or
2) Wrong sizing of filter components. Poida did all the legwork of figuring this out. Warpspeed contributed imensely as well, take a look at this thread if you havent already done. Resonant frequency can be a killer of the best bridges (road bridge) tacoma narrows, let alone an inverter mosfet bridge.
https://www.thebackshed.com/forum/ViewTopic_mobile.php?FID=4&TID=9409&PID=122471&LastEntry=#122471I certainly dont know all the answers and im not suggesting you need to invest much time in it. If there is evidence of an unexplained problem though, it can be worth it to make a change to the choke or cap to see if things improve. From reading threads it appears like some have had transformer/choke sizing that continued to eat mosfets regardless of the inverter boards until changes were made. I do think there is a solution that will make it indestructable for normal use.
Glad u got her running again!