Yeah it can be a bitch.
I remember putting a closed wrench on the bottom nut and the letting the wrench rotate against a strong metal part underneath to hold it'self in place (access towards the front wheels). Then you can just use a socket wrench to crank the adjusting bolt.
I had to use an open ended wrench on the locking nut (approach from the rear wheels). You'll only get a slight turn, then you need to flip the wrench over, and turn again (still approaching from the rear). You're only doing like 1/32 turns, but eventually it loosens up enough to use your hand.
Also lots of liquid wrench is VERY helpful.