That's a nice idea.
Have certainly noticed that robos like digging/tunnelling. Our 2 have a load of carefresh for bedding and on top of that we shove in a handful of shredded paper in their main nest. By clean out their nest is a solid mass of bedding with a hole in the middle (they can often be seen poking their heads out the top or side) and they build up mounds of bedding against the side of the cage (very glad they live in a duna) so they can burrow in that.
They get toilet roll tubes as well but had never thought to actually place them under the bedding.
