I'm building cabinets for my basement wood shop and need your advice related to the joinery.

FWIW - I'll be using 3/4" plywood to build frame-less cabinets which will sit on castors so I can move them around easily and potentially use them for infeed/outfeed support. I'm thinking of making them 36" wide but am open to suggestions if this would be prone to sagging.

With regards to the joinery, Kitchen cabinets have the top and deck between the left and right side panels; however, I wonder whether this is the best design for shop cabinets which will need to support a modest weight while suspended between castors rather than sitting on the floor? Will dominoes or pocket screws support it in this configuration? Should the top/deck be flush to the outside of the sides instead? What about the back, should I rabbit it into the sides with butt joint on top/deck or just use butt joints all around with dominoes/pocket screws?

I don't intend to put an enormous amount of weight on top of them but need them to be able to support a modest weight without sagging while also having shop items in the drawers. Thoughts???