[the fan that brian (T-back) used.
a breeze makes a huge difference so i guess when you find your only choice for hammocking is sometimes in hotter times than you'd like, it may be worth it's weight in gold<g>.
if someone wanted to get technical about it, some questions to consider might be...
1) most efficient fan blade type
2) best motor size & battery type to get the best air flow for the weight.
3) light weight, adjustable attachment methods (small wire?).
I've been using a coleman tent fan for about 3 years now. It started out weighing a whopping 1.7 lbs but I have trimmed it down to 2.2 ozs.
It will run, in my experience, about 20 hours on a "d" cell battery. I have switched mine over to a "aa" battery but have never timed it to see how long it will last. I've used it for four nights before and it was still going strong. I hear you on the summer night heat! This little fan puts out a surprising amount of air and it's possible that you could hook it right on the zipper where the slide closes, though I'm not really familiar with the WB closure. I think that a hammock with a fan is the ultimate outdoor summer bed as you are not laying on a mattress to insulate and prevent the cooling of your back. I usually run the fan until it's cool enough that I'm not lying in a pool of sweat. I try to take some type of bath at night just before I turn in. If i'm not near water, I will wipe myself down with alcohol which has the dual effect of killing skin bugs and cooling me off. That plus the fan makes all the difference in sleeping in the heat after a long day of hiking. If you would like pictures (of the fan not me bathing ) let me know.
How's the planning going for your hike?