Russ, here is a tip for those hot burning days. When I sometimes do aircraft shoots, and have access to the ramp, I need to stay in one place, or near it most of the time. I take a chair, and a golfers umbrella. This serves the purpose of keeping you dry if it sprinkles, and more importantly keeps those hot sun rays off of you creating some shade. When I go out to shoot trains I take them along also. Chair is used more if there is a wait involved and set-up too far from the car. I just did an aircraft shoot on a hot day, and only stuck around 2-3 hours due to the heat. Seems like when the weather is cooler these guys don't fly much. Same for steam excursions, usually in the mid-summer. Thats why the Narrow Gauge is a great destination, as its always a bit cooler and drier(Humidity wise at least), in D&S and C&TS land.
Greg