use titebond wood glue...
go ahead and use at least two screws for the ends of each bracket...just get the screws long enough so that they go through the bracket & halfway through the sides of your cab...mount them from the inside of the cab...that way no screws will show from the outside & the screws will help pull the brackets tight so the glue can get a good bond...
you'll want to drill the holes through the brackets so the screw slides though the hole & only screws into the cabinet sides...ideally you'd want four screws per bracket evenly spaced to evenly apply pressure for the glue to take hold...