Another thought on the tires...
From everything I've read a MT is less than ideal for the type of conditions you are planning to use them in. I was once told that the best tire for driving on the beach was a bald street tire, reading since then I understand why. In sand you don't want to dig because you'll never find the hard bottom, digging is what mud tires do best. Instead you want a tire that will float. A bald tire with no tread isn't going to dig, unfortunately it isn't very safe for road use either. Seems like the best tire for loose sandy conditions like dunes or beach would be a wide all terrain or highway tire. On top of that lowering tire pressure when you hit the sand would make the contact patch even larger which would make them float on the sand even better.
Just off the wall thinking here, no basis in experience. I said previously that a wider tire is better for sand. It's possible that a taller tire might help on sand as well. Moving to a taller tire is effectively the same as going to a higher gear ratio which means that you will loose acceleration and pulling power, the added weight will add to that as well. That sounds bad, but softer acceleration means you are less likely to spin tires. Spinning tires means digging and as mentioned previously digging is bad on sand, so a taller tire might be beneficial. That's just speculation though.
I can speculate a lot, but best thing you could do for selecting off road tires is talk to people that play where you want to go and see what works well for them.
Here's a better pic of my truck on the 32s like I said I'd find.
With yours being a step side and no flares, I can tell you that a 31x10.5 looks good on those as well. That's the size my dad has on his step side Ranger, sorry no pics. If my Ranger hadn't come with the flares, it probably would have stopped at a 31.
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