IT sounds like you need a filler panel? Or, you could insert some sort of tray storage or spice rack? Are these new cabinets or are you retrofitting?

You could also look at drawers -- I know you can get 27" wide and am trying to remember whether I've seen 30" -- but 27 would be within a trim out range. If you are going to have 6-15", I would all a drawer, an ice maker, shelves for cubbies, something useful depending on where your space is located and the use it will get.

I have a 36" refrigerator cabinet but only a 33" fridge. I wanted the cabinet large enough to accommodate a larger fridge if we bought a new one later. We ordered extra trim pieces and our contractor trimmed out the opening of the refrigerator cabinet to make the opening 33" for now. There is also one along the top since I made the opening large enough for a slightly taller fridge too. Since this is the fridge cabinet, we didn't use overlays but if your cabinets next to your opening have drawers or doors, you can also put an overlay over the trim piece to match the doors.

Here is a pic of the fridge: {{!gwi}}From Kitchen