Convert to a Transit stud pattern and use twin normal wheels.
Assuming you have enough stud axle length to accomodate the massive offset.
Use normal road wheels, but mount in front and behind them a set of wider Off road wheels/tyres, but lifted up about 2 or 3 inches. These could be bolted direct to the trailer with no suspension.
On the road, only the road wheels will be in contact with the surface. - Legal.
On the soft stuff the road wheels will only sink in a couple of inches before the 4 wider wheels take over and spread the load.
Best of both worlds?
RIBBED For extra pleasure.
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