I must admit, I don't leave any test gear in the truck in winter, it isn't good for the kit, plus as we've seen it can be dangerous due to condensation. I have heard of MFT's either giving incorrect readings, or actually being damaged by being brought out of a cold van in the depths of winter and being asked to do a loop test right away. I put mine in on leaving home, then take it straight out at the job, even if it's a couple of hours before I need it, at least it's at room temperature.