Just thought of this and will have to try it out. First, lash together a square frame out of timber. After, insert it into a bivy sack. Then, tighten the drawstring, or zip up the entrance. Finally, hop inside and paddle your improvised kayak to your destination. I was also curious if I could make one of these out of 12" diameter PVC pipes and my goretex bivy. Or even use PVC pipes and a large drybag type backpack to build an ultralight riverboard that you can store your dry gear inside and carry on your back.