I built my till with a 3/4" carcase and a 3/4" back rabbeted in the back with glue and highpoint screws. The back attaches wall with a, 1" thick french cleat that is glued and screw to the back panel and a maple backer panel on the inside surface of the carcase (maple-ply-maple). I over built it like crazy and it's not the prettiest till , i would do it the same way again. I dont really see the need to skimp on material when the tools are so valuable- play it safe. There is a signifigant investment in those tools(one that i cant replace) and the thought of them falling to the floor sends shivers down my spine. The way it's built i don.t even think twice about the amount of weight in there.
I was going to put hardwood edging on the surfaces of the ply endgrain on the front, but never got around to it (and probably never will). I am planning on moving shops in the next month or to and MIGHT get around to building a door with space for saws and layout tools.
"Aus so krummem Holze, als woraus der Mensch gemacht ist, kann nichts ganz Gerades gezimmert werden."