AW had spoke problems with 20" wheel. Radial laced But that was a stock 9c rim and stator I sent him. Surely it can be done stronger.
I have wondered how nice a FS longtail you could make with a nice strong scooter wheel with a cast rim and fat tire. Get that load as low as possible. Mine carries too high, and you do feel it. I try to put all the heavy shit in the lower panniers, water, batteries, canned foods, milk, beer. The big upper boxes high on the deck carry the lighter stuff in the grocery bags.
Loaded for touring, all the extra camping gear ends up loaded very high and makes it harder to ride. But touring I need to ride slow to extend range, so it's still tolerable enough.
In the end, I just put the longtail on a trailer, and camped in my car when I did what little touring I did this summer. The place I wanted to ride was 150 miles away. That made the riding I did much nicer, loaded only with battery. It was nice to carry a generator in the car to charge.