Yes, I was thinking about either use moss on the side, or bark. Also If the spray bar of a filter is on the top, then one would be able to use stem plants to hide the box, this would allow fish to seek protection under the box and maybe even use the plant media as more filtration.
I have a small tank I can use this on, so will try with a prototype and post photos. The hard part is to get a box with legs. Will have to improvise, either with a flat log with legs made of acrylic rods, and the box secured on top.