For a tractor in W NC, you don't *need* insulation, but it will make your life a lot easier (in a tractor especially -- b/c you will [hopefully] be having somewhat proportionately more airflow than you'd need in a full sized coop). I'd do it. For a tractor I'd use foamboard covered with thin plywood or thin panelling or that sort of thing.
For a tin coop in TX, the main value of insulation would be just to prevent condensation on those few days when the temp gets down near freezing. I'm not sure it's worth it. It never *hurts* to insulate of course, but I'm not convinced you'd get much value out of it. Doubt it'd keep the coop any cooler in the summer -- shade and/or ventilation would be much more helpful for that.
Good luck, have fun,
Pat