I use an IGH with a MTB freeride rim...between the beefy rim and symmetric build it's bomber and hasn't needed any attention on my Dummy. I've carried two adults on the back as well as my GF and 100L cooler full of beer and ice.
In terms of your wheel issues...was the wheel machine built and if so did a wheel builder go over the wheel at all? It's possible the components were up to the job, but poorly tensioned.
If you don't want to go the IGH route I'd get a 36H heavy duty MTB freeride rim and get an expert wheel builder to build it up for you.