Attach two full-extension glides to a small wooden platform -- one platform for each slide-out pantry unit.

Position the first platform, hardware side downward, on the bottom of the pantry cabinet. Drive screws through the glide/slide rail into the floor of the cabinet. Repeat for the second shelving unit.

Position and install an additional slide/glide mechanism for each sliding shelf on the top panel of the pantry cabinet. Attach the glide to the underside of the cabinet's top panel first. Set the shelf in place and attach the glide to the top of the sliding shelf. You will have one top glide attached to each shelving unit.

Drive screws through the bottom of the shelf into its platform at the bottom of the cabinet. Install the second sliding shelf in the same manner.