While roof vents, exhaust fans, and air conditioning units will go a long way toward keeping you cool, you should never forget your basic, old-fashioned methods. Whenever possible, park in the shade. Open your windows and doors. Keep a damp towel wrapped around your neck and fans blowing on you. Use misting water bottles. Stay hydrated. And be smart. If temperatures in the truck exceed 91 degrees, take extra precautions. If it gets to 100 or more, you should probably close shop until things cool down.