I've been going back-end-forth on the foot box thing. I have a camp quilt that I purchased from Campmor, not very insulated, good enough for chilly nights, but not when it starts getting cold. That's why I decided to make a lightly insulated quilt (Apex 3.6), this should take me from the 50's to the 30's with no problem.

The Campmor uses mating ties to close up the bottom and/or side, that way the foot box isn't permanent, so in the warmer temps I can keep it open. Problem is that there are open spots that might let the cold in when the temps drop. I've been tossing the idea of velcro (least favorite, it does wear out), plastic snaps, or a zipper (close the bottom and about a foot of the side).