Aluminum panels of same thickness would be much heavier, and transmit cold and heat rapidly.. I measure current plywood at 4mm. (.158"). And don't know type of this used in 1999 when mine was built. Has white laminate on face.
Tubing used in post on this forum " This Old Granby Build topic 10761 is interesting, but have not seen followup of it. And, wonder if emt is subject to bending and or only having 4 points of attachment to carry weight is enough. Or that 3/4" tubing is too thick when folded on top of mattress?
High strength aluminum sheet, (6061 T6 or 2024T3), .125 skeletonized out with large lighting cutouts, big enough to let one stuff sheets of Prodex insulation behind it might work? Seems a lot of the resistance to bending strength of the plywood is supplemented with the aluminum extrusions riveted to front of lower panels. These would be needed on .125" skeletonized aluminum plate also, IMO. Aluminum much more $$$ then wood. Having openings in panels to clean behind them, (mold, mildew, condensation), is a definite advantage.