Insert the Cabinet
If new inside-mount cabinet is larger than old one, have a helper help hold it in place and outline it on wall.
Use hacksaw to enlarge hole and studs, if necessary.
If wires and plumbing are inside wall, hang surface mount cabinet instead.
Out of 2x4 boards, cut horizontal and vertical framing for new opening.
Glue horizontals at top and bottom to studs.
When glue is dry, secure horizontals to studs with wood screws.
Vertical framing should equal height of cabinet. Toenail verticals into studs.
Insert cabinet in opening and screw into new framing.
Install childproof lock on new cabinet.