pic: new design

It’s likely you have already heard this, but you should probably put some cross braces between the toughboxes.
Assuming that the baseplate doesn’t flex, you will still see alot of flex in the KoP angle brackets and crossbraces will help with that.

You should also put something outside the wheels to support the axles and keep unwanted strain off of them and the gears.

We have been using direct-driven, cantilevered mecanum wheels in parades, demonstrations, practices, and Breakaway(with frequent bump crossings) for 2 and a half years with no ill effects.
Just remember that keeping the wheel close to the gearbox will minimize the torque on the shaft.

Yes we already had put in the Cross braces for the toughboxes