How about using basically any good tent... and then over it stretch a green poncho. For me this might be a little pup tent (light, cheap, enough room, can use sticks as poles....) with a $2, works-fine-but-if-it-gets-trashed-it's-no-tragedy, probably needed to carry it for something else anyway (I've never had too many ponchos. Or enough) poncho lean-to'ed over it. Not really "hiding" -- it's just a little extra rain protection that happens to be green, but not being too obvious, either.