The best place on the 727 to warm up was actually underneath, where you could sit in the pack heat exchanger exhaust on the belly. The 727 had HUGE pack fans to keep them cool on the ground, and there was a virtual gale of very warm air comming out even when they were being used to heat the ac. Both sets of heat exchanger exhuasts were on the bottom of the AC, very close together. Best thing about it was it didn't smell like APU exhaust. In winter, it would actually melt a spot in the snow/ice underneath, and dry it out.
This assumes, of course, that you had the packs running.
One time I got the drenching of a lifetime in MDW doing the walk around. I mean I was soaked to the bone and it was cold out to boot. I sat in that spot for about 10 minutes. It was like one of those hand dryers, except for your whole body. After 10 minutes, I was totally dry.
Doug - man, I know what you mean about those MSP walkarounds...brrr. Be sure to get some Caribou to warm you up. Much better than Starbucks, IMO.