I was just reading this post and came up with an idea for those who have already bought the penguin filters and like that clamshell design posted about earlier. Couldn't you just take two old filters, remove the carbon and sponge/floss, then staple/attach them somehow on the bottom, facing each other. That way you can just make your own clamshell that will fit, using old parts, that you can stuff with any filter material you want? Just a random idea I just had.