I've Modded one of the original pattern MOD bivi bags to be a single hopped bivvy with a wide zipped opening and midgie screen. It requires a lot of patience and someone good on a pretty hefty sewing machine. Looking at everyone else's reply I can see peoples concerns with piercing the bivvy bag but as long as all the seams are sealed with good sealing tape it's fine. Ain't had a leak yet. Point north provided all my kit, rod for hoop, extra gore-tex, midge screen and sealing tape. If you haven't done it already iron the sealing tape on using a piece of printer paper between the tape and the Iron. Last bit of info won the hard way!