Best thing I can tell you if you already checked all the fuses (in both boxes I assume?) is to hit the Hummer dealer in the morning before you leave for your trip, or go to one when you get to where you are going. Seems to me like the unit itself needs replaced if nothing works at all.
What really strikes me as odd is that you got your H2 detailed before going on a road trip. You do know it is going to get filthy 15 minutes after you get on the highway.
Sorry to hear about your problem, the timing really sucks as well.
