Yes, scrambling around under the car on cold concrete with wind whistling through all the cracks in the door is never much fun...
Yes can sympathise, last house had the up and over doors, really drafty. We replaced the current garage up and over doors with roller shutter type. Amazing difference, pretty well draft free. I also use old collapsed cardboard boxes, large ones, and old carpet remnants to keep out the cold of the concrete floor, works well for me. I also bought a small propane space heater which allows the garage to get to a tolerable level in a short time.
Peter