I went out in my backyard aka mountain forest and found some neat looking limbs with knot holes and such. i'm going to wash them off and put some moss on them and do shrimp. good idea and not sure i hadnt thought of that already.
on a side note, i had taken some floating sprite from the tank side and floated it in the boxes til i got some rock and weights. well, tonight while feeding i saw something move in one of the boxes. it's a baby fish! wow! gonna try to grow it and see what it is! yea! so neat!
I like the driftwood look. Have you considered keeping a tall, narrow plant like crinum in there too?
You know, I think you could potentially keep some very small nano fish in those, like chilis or other microrasboras. I normally wouldn't keep them in a 2g due to issues with maintaining water quality, but since they have the benefit of the stability of the large tank, you could probably keep a half dozen in one overflow box (assuming the hole isn't big enough for them to escape through, might require the addition of some mesh over the hole). You could still keep small shrimp with them too, since the shrimp would mostly occupy the floor or climb the hardscape.