Tire Pressure for Sunfish Dolly Wheels

While I live a the shore, my place is still nearly a mile from where I can launch the sailboat. So to get to the water, I have been towing the sunfish using a tricycle (a Taga to be specific) and the Seitech dolly that has the standard 5x14 wheels.

Does any one know the max tire pressure I can put in the dolly tires so that I can make it easier to tow?