They are hydroponics trays and reservoirs. Made of abs which from my research seems to be reefsafe. They are also built to hold water. I was looking into the Bonticare brand 4'x8 tray and the 100g ezdrain. The 100g was not flat bottomed but was deeper with smaller footprint. You will need to search to find the place with the best shipping to you. Here is a link to where I was looking. Shipping was better with 8' because it wasn't thru ups.
http://eastwesthydro.com/category/hy...raysreservoirs