If they can be hidden by a front lip on the shelf, or the customer doesn't mind seeing them, we use good quality double faced tape to stick them to the bottom of the shelf, or the bottom of the cabinet itself. Hiding the xfmr and making the line connections in a box have always been my headache.
The "pucks" we use (WAC brand) have about 30" leads on them, so we use them as branch wiring, and use those tiny tap connectors to tie them together
