The air intake sits on the passengerside, about 12" behind the headlight right at hood level.. So I'd guess if that stays dry, you can go that deep.. Maybe 3'.
It would be interesting to run with some Hummers. I wouldn't be worried about getting stuck, I'm sure one of your rigs could pull me just about anywhere.
On the class IV roads I've been on, I don't think a hummer could make it though.. the trails are just too narrow.
I'm in Nashua, but have only hit the trails up in the central part of New Hampshire.