Good idea going with a 20°F bag. I have a summer weight bag in my truck with the idea of layering with blankets. But I've been rethinking past East Coast and PNW winters, and then visualizing the mountain passes of NOCAL and Southern Oregon. A down bag may be more appropriate -- not cheap but they do look comfy. For indoor/in-car use, down should not be a problem.
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Better is the Enemy of Good Enough.
Okay, what’s your point??