I am 250 and built like a linebacker. I still hit the weights at least 3 times a week and i have trouble zipping mine up, so what i do instead is, lay the bivvey in the bottom of my hammock with the green bag inside of the bivvy the way it should go. I then slip my black bag, upside down, into the bivvy making sure to put the footbox of the green bag into the footbox of the black bag. This way the black bag is laying on top of me like a top quilt and i can get the bivvy (its a tad bigger then the other two bags) and use that to Zip up. I also use a thermarst Z-rest in the middle of my Claytor Hammock and have yet to have this fail to keep me warm, and i live in the beautiful Pacific Northwest where we get lots of liquid sunshine and nice brisk evenings with liquid moonshine. LOL Its wet here even when its dry.
I wear a 48 jacket, but I'm still hovering around 200. If someone at 230 can get it zipped, I'd imagine that I might have a little more wiggle room (literally and figuratively).