Materials: Heavy Duty cardboard box, single sheet of foam core board (Wal-Mart), cake board (the size you need), exacto knife, glue gun, ribbon, scissors and tape.
Use cake board as your pattern, trace over foam core board.
Carefully cut out, don't try and go all the way through the first time just get it going and then go over the cut again to complete.
Use the foam core board you just cut and trace over the cardboard box. This can be double or single layered. Here I cut through two layers of cardboard because I'll need four since it's a heavy cake. This will hold one, 6, 8 and 10 inch fondant covered cake.
I placed the two cardboards in between, foam core on the bottom and cake board on top. The foam core board supports REALLY well.
Cover with cake foil.