Some use paper towel rolls, I use the cardboard cup holders you get from McDonalds. I have also heard of cardboard boxes being cut up and one sid ripped off leaving the rippled side showing to allow more surface space. Hope this helps some. Also you can always go to a breakfast place like IHOP and ask them for their old disgarded egg crates. I have done that too.
... Sorry didn't see the Washable part ... long day at work.