I have done it with my emperor media baskets. If the Penguin design is similar, it is a pita- you have to cut sponge strips for each of the sub pockets.
You may want to look at a new cart now available from DrFosterSmith.com. I am messing around with it - I dont use their floss/carbon insert but instead cut a piece of rigid floss and use that with the supplied sponge and frame- seems to be working well. I replace the floss weekly.