For our old but new to us one we decided to attach a layer of melamine to the inside top of the shelves. Since ours has heat cable, we could not just add it to the bottom of the shelf. We are using Sterilight tubs with ours, and they are a little taller leaving a little less gap. I also contemplated adding melamine up to the heat cable groove, but that would leave more air in between so not real sure about that yet. I will let you know how it goes. This is a weekend project for us.
*Fila*