Park it in the sun. Even at 50*F, it will loosen up a lot.
Yep, my strategy for these has always been to grab a friend and a sunny day (even 45 or 50° if that's all you got) and PULL LIKE MAD. It'll still take about a half hour of real effort to close it that first time if it's only 50 out. Stand, sit, curse, whatever it takes.
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