The only complaint I have about Paperclay is that it doesn't like to stick to much of anything (even itself sometimes). I'll bet I'm doing something wrong, but I'm a tad disillusioned by this "awesome material" especially since it cost so dang much. I'm sure it'll work out okay though, and it does sand very, very well.
After I sand some more, put on some more Paperclay, and then sand some more, I'll be putting on at least two layers of Modge Podge to seal and prime it. Then, I'll move on to paint. Painting will be interesting. I've never done a prop with metal-looking pieces or done heavy weathering.
I've also started blue prints for the main body of the "med pack"/backpack. I'll be making most of it out of foamcore and the extra bits will be out of foamies.