Pretty cool idea. These custom backgrounds really intrigue me lately. I have a center overflow I would like to cover up one day. This could work for that too. Never seen it done on a floor though. Curious to see how it looks when done.
They have overflow covers.
I was told that the weight of the water will keep it down. It's not the traditional Styrofoam background material. It reminds me of roofing stuff.
i wouldnt cover up the whole thing with sand, besides i just said what I would do, dont get all offended bro.