I made one myself a few years ago. I believe the YouTube video that explained the process was something called the “Freecoy” or something to that effect I’ll see if I can find the video later. I used thin panel board and then cut into small segments and reassembled infield using a few nuts...
I have black Ovis and really like them. I had a little issue with the top not cinching down quite enough when we had to wait a few days to be flown out in Alaska. We ended up using string to tie them up which was fine but since then I carry rubber bands for each for convenience.