Just a thought here, thinking back to a thread I started about using racks from Lowe's that had pressboard shelving. Adam suggested covering the shelving in heavy grade aluminum foil (the type you would bbq with). A couple of layers, shiney side up would reflect the heat back up to the cage, heat that might be going into the wood that Robin's cage is on (therefore saving in wasted heat loss) and also protect whatever wood top this cage is on from scorching/over heating.
Make sense to anyone else?
~~Jo~~