hi-
excellent idea yeevia!
when i use an open tub i like to use a chunk of styrofoam- like you get in shipping boxes- i poke a few holes in it to root cuttings from my houseplants at the same time lol

funny i think tho- for years i never added anything for the nest- they made it under leaves and plants always- but when i add styrofoam or a cup etc- they always want to use it! you would think they would prefer something more natural- but i guess it is stronger and better lol.