I don't know if you have bought your tent yet, but If not, pay attention to ventilation. I know this because we are in the laborious process of choosing a tent and bought a copy of Backpacker magazine's 2011 Gear Guide. The Marmot Boreas 3P is reviewed as 'best ventilation'. 'like sleeping under a celing fan'. Since our camping will be in desert southwest and Big Bend this will most likely be our tent.
Also, some years ago camped down on the river in Big Bend and it was 103 degrees at midnight. I told my husband, "this story has two endings: one, it was the most miserable night we have ever had, or two, we packed up and went home. So which ending will it be". We packed up and went home to Ft Davis. Being older, wiser, and with slightly more jingle in our pockets, we will be buying summer stuff, not the tent, sleeping bags, etc., rated for Mt Everest!