One other thing you might think about, if you are sure that there will be trees at your camp site, is a hammock. The people who have the Hennessy hammock seem to like them.

http://www.hennessyhammock.com/index.htm

I don't have one, but I have been staring at the web site pretty hard. They are small and light. I'm under the impression that you will lose a lot of heat, being up off the ground and all, so you might want a light sleeping bag even in the summer (or not...). This rather negates the weight savings, though, doesn't it? Sigh.

Anyway, it's another option for you to consider.