Whatever you use for legs, Make sure youve got adjusters in the bottom.
Weve used simple 2x2 legs with T nuts in the bottom for levelors with Model Railroads.
Drill a hole in the bottom, Pound in your Tnut and use the screw inbolt to compensate for uneven ground.
Considering your situation I'd try to set it up while on level ground and then give aprox 1" In and 1" out as an absolute Minimum for compensation (1 1/2" each way would be even better) This would require drilling your hole 3" deep
Another alternative if you think things may get more severe is to attach a Piece of 2x2 16" long to another 2x2 and drill holes every 1/2" and use carriage bolts...........Use the T nut in the bottom for fine adjustments.(You could go to a smaller length tnut/bolt this way...say 2" with 1" adjustment either way)
By doing this you could have a pothole under the leg and still be able to compensate!!