I don't know about making one, but there are several good shooting rests out there that are cheap and easy to transport. My favorite is one that attaches to your tow hitch. Try Cabelas, BassPro, Sportsmansguide.com, and Cheaperthandirt.com. I'm sure you'll find something you like. At the very least, you should be able to look at how they're made and maybe come up with your own design.