I am planning a tool cabinet as well. I am eager to see Paul’s tool cabinet build before embarking.

Robert Wearing’s The Essential Woodworker  gives some good details and illustrations (pages 153-165) in cabinet construction.

One example shows a rebate cut only into the back edge of the cabinet sides, about 2/3 – 3/4 of the thickness of the side, to the full thickness of the panel. Screws are then installed at a slight outward angle through the back frame. This method requires the dovetails at the back of the carcass to be offset back the edge to accommodate the deep rebate, which weakens the joint slightly. Another example rebates both the sides (to half depth of panel) and also on the framed panel, which avoids the offset dovetail.

Hope this helps. I highly recommend Wearing’s book.

There is nothing wrong with using plywood for backs of some cabinets, just not furniture pieces you sell. Plywood is fine for rigidity and strength. I would apply a couple of finish coats (either paint or varnish of some kind) if I wanted the plywood to resist the ingress of moisture to the sub fibres. This adds longevity to the plywood. Back in the sixties salesmen told is plywood lasted longer than real wood which has proven not to be the case in general, unless you use a high-grade marine ply. Plywood is of course fast and effective. many woodworkers used plywood to skin the front and back of their joiner’s tool box and then painted the whole thing black and this gave a neat appearance. trouble is now, I have seen these tool boxes with crumpled plywood facings three and four decades later.so I probably wouldn’t use it for my personal boxes.