On St Hammer wheels (diameter 500mm) i use Car trailer stub axles, these have taper roller bearings and they have had no problems with the punishment they get.
On the new Saint i have a 10:1 gearbox driving cart wheels, i am putting a Technobots 30mm 4 bolt cast flange bearing, between the gearbox and the wheel as close to the wheel as possible, to try and stop the gearbox bearing from being destroyed.

Hope this helps