I ran trails there last summer and took no damage other than a few scratches from overgrown brush. A stock Xterra can handle a good part of the park, but I'd recommend having one or two "recovery" vehicles along. Someone with a winch and mud tires that can pull you out if you get really stuck.

One of the hairiest/most fun trails I did was the Orange trail (I think) near the park entrance. Very tight and twisting, but I drove through it with no damage when it was really muddy.

Beware the tubes, only try the shallow side and check the depth before attempting. You could easily swamp a truck if the water is up. I dropped out and my sliders hung me up on the corrugated pipe. I had to get tugged out.