I was fortunate enough to be given a Sierra Design Clip Light 2 man backpacking tent by a friend when I first got into backpacking. Unfortunately I have been having a hard time finding a footprint for it. I currently am carrying a pack upwards of 40 lbs. and want to cut weight as my backpacking adventures become longer and more intense. I was hoping to gain a little insight as to the groups general opinion of bivy sacks. Love them or leave them? How do you feel about the use of bivy sacks? Got one in particular you recommend? 4 season? Lightest?