17 FREE Cardboard box "coolers" (designed for ice packs and keeping items cool [such as refrigerated medicines]), but also useful for secure padded packing.
OUTSIDE box dimensions: 12"L x 10"W x 11.5"H. Inside box cut-out dimensions: 7.5"L x 6"W x 7"H.
Or, you can throw away the corrugated cardboard insert and just use it as a heavy-walled (e.g. book packing) box.
I can also give you some of the (still frozen) disposable "ice packs" that came with these if you have any interest in those. They fit into the inside opening and were stacked around the original contents.