I actually got it from Lowes...not Home Depot...but I assume HD has it too.
it is called Plaskolite corregated plastic.
the link is here...
Plaskolite
its is a good sized sheet and I found some smaller ones that day. You can see on end that it has the corrugated channels.
you can easily cut it with heavy scissors or a box cutter.
I cut out about 4 or 5 two-inch squares and superglued them into a stack. I then put a piece of stone tile (that I had lying around) with some superglue to weight it down so it did not float. any stone or river rock or reef rock would do.
the little corrugated tunnels seem to be perfectly pod-sized. it ends up being a breeding area.
Every so often, I retrieve them and shake it into the DT and they spill out.
I put about 3 or 4 in my refugium and it seemed to work great.