Entity sleepingmonkey1 spoke thus:

> use this stuff called sintra or polystyrene.
I know what you are talking about, backing board. Its too compressible.
Haven't heard any good ideas so far, but maybe browsing Home Depot is a good
idea.
 I was hoping for some material that is like plastic with a lot of ribs in
it so it's not compressible.

Guess I'm the first to do this!

-- Rachel