Sounds similar in shape to one of my ideas. The other idea is a half vestibule - or actually about a 5/8 vestibule, which would be reversible. I'd pitch it on the end that seems likely to be into the wind, just to give a little shelter for muddy shoes and a way to protect the door when getting in and out. that's all I really need, since I have found it comfortable enough to fit two guys and our gear into the tent. Ideally I'd make one like you made AND the half unit, and use whichever suits the trip best. But the real question is do I go for the old reliable silnylon, or spend some green on the spinnaker to save a little more weight?