Cut a strip of cardboard 25 inches long by 12 inches high, using your box-cutter.
Measure 12 inches from the left side of the cardboard strip and make a mark using your pen.
Measure 1/2 an inch from your mark and make a second mark. The space between these two indications will be the spine of your record sleeve.
Measure 1/2 an inch from the right side of the strip and make a final mark. This last half inch will connect the two sides together.
Cut one more strip of cardboard to be 11.5 inches by 1 inch with your box-cutter. This will now function as the bottom of the record sleeve.
Glue this strip to the bottom of the left side of your record sleeve using your epoxy. Once it has set, fold the strip in half from the bottom onto the top, so that you have two .5 inch sides.
Fold the sleeve along the marks you have made so that you have two 12 inch sides, a 1/2 inch spine, and a 1/2 inch catch at the bottom.
Coat the strip on the bottom of the sleeve with epoxy. At the same time, coat the 1/2 inch spine on the open side of the sleeve in epoxy.
Press the two sides together so that the tabs on the bottom and the right both press on the inside of the sleeve. Cover with a heavy object until the epoxy sets.
Paint your album art on the outside of the sleeve once the epoxy has set, and you have a hand crafted, hand designed cardboard record sleeve!