Plywood Cases
Build a rectangle from plywood strips a little wider than your gun is thick and slightly larger than the gun. Use 1/2-inch plywood, and nail the corners with a pin nailer and wood glue. Cut plywood panels to cover the top and bottom of the rectangle and nail them on. Cut the rectangle frame in half, using a table saw to cut around it to release one piece for a top. Hinge the pieces together with piano hinge, and add a handle and latch with a hasp for a lock to complete the case. Use latex paints or wood stains to finish the case.
Tool Cases
Cut out the foam or plastic molded inserts from a tool case to make room for your gun. Select a case with a good handle and a latch that has a hasp large enough for a small lock to secure the case. Use a wood burner, or soldering iron, to cut along the plastic edge to make removing the interior easier. Use sand paper and spray paint to refinish the outside of the case. Use at least two coats of paint, allowing drying time in between coats for best results.
Foam Inserts
Cut enough 1-inch thick foam sheets the same size as the interior of the case so that when stacked, they will fill the case. Lay the gun on one foam piece and trace around it with a marker. Cut out the traced outline with a utility knife. Make a second cutout piece. Lay one solid sheet in the case. Stack the cutout pieces on top and fit the gun in place. Apply spray glue in between layers. Fit one more sheet of foam on top.
Locks
Fit a small combination padlock into the hasp on the case's clasp to secure it. Choose a combination lock with the largest available numbers for ease of access in emergencies. You can also use a keyed padlock. Hide the key in a secure nearby location so that it is always within arm's reach of the case. Keep gun and ammunition stored separately for optimum safety from children. Always lock your gun in its case when it is not being used.