Before I sent my first book mooch, I was trying to figure out an economical way to package the book. What I really wanted was one of those little sleeve things that Amazon uses when they send out books and other small rectangular objects. But all I had was some cardboard … here's what I did:
Gathered up all the stuff … cardboard, book, tape, utility knife.
Cut the cardboard so that it comes up over the short edges of the book with a decent lip (the width of your packing tape or more) and so that it comes up over your long edges and overlaps with some to spare. Then place your book in the center of the cardboard and cut out the excess in the corners as shown.
Fold in the short sides and then one of the long ones. Tape the long edge to the short ones. Don't skimp on packing tape.
Fold in the last long edge and tape shut. Add tape as necessary to close pretty tightly.
Put return and sending address on with your handy-dandy sharpie.
Take to your local post office and send via Media Mail for under $3.
Your wallet, the earth, and probably your book moocher will thank you. 
Genius.
Very, very clever!
Very cool and I love the illustrations too!