I'm got a ton of work lined up to repair my old cody style jetpack (major smoothing problems).
The 501'st has some measurements that I laid over some images to get a rough template. Once I had that, I made the base out of stacked layers of 1/4" foam I found at the dollar Tree and then coated the entire thing in Bondo Glass. It was left unfinished, now I'm going back and filling in and smoothing (smoothing was pretty bad, I was 16 and had never worked with Bondo glass before). It's ultra light though at just over a pound without the engine. I figure that by the time I finish fixing the many surface issues and installing a new engine it will be 2-3 lbs.