If you want to camp on the backside of the dunes, head north on 95, pass Valley View on your left (you have to look off in the distance for the green street sign), then you'll see the BLM's "Big Dunes" sign. About a mile or so north is where you'll make the left. It's a nice(r) graded gravel road in. Drive in about 3-4 miles in, and you'll see a wooden fence post structure...make a left there, and you'll have no problem finding a decent-ish camp spot.
If you want to camp on the front side, make the left on Valley View, and go about 2 miles or so. You should see a dirt road on your right heading into the dune area. Forget that one, and continue on VV for about another 1/2 mile or so, and make a right at the next dirt road access. Wind your way in, and find your special place. It's not that bad, it's just really silty in some spots. You shouldn't get stuck, unless you want to. Good luck.