Don't be afraid to air down to 10-13 lbs. You really only need about 5 lbs to keep the bead solid. The lower the air, the easier it will be. Front and rear - not just one or the other. A 20 is too high for loose sand. I used to run at about 15.
I once came across a camaro in the deep sand in Corolla. The guy went to the beach along the packed sand along the fence. But for some reason, decided to try the deep sand on return. I couldn't do anything for him since he got down on the frame and no where to safely attach to.
Remember, people were running the sand before 4x4 came along. Their secret was low air pressure in the tires - generally around 8 lbs.