Hi Glupson
If you read some of Johnathan Skull's writing (I think it was he) he used cardboard boxes partly filled with newspaper for trapping his corners. Cardboard and newspaper (not so much slick print) can be fun to play with.
If you ever run across me talking about making pressure boxes, the originals were cardboard. Tons of uses for compressed paper, or even loose crumpled. Sometimes however cardboard and paper can be a curse in a system, especially if you live in higher humidity.
Btw thanks for your questions and being patient with me many times. Sometimes when I'm up here I barely have enough time to squeeze out a few words before needing to run, and I appreciate it very much when the questions are clear and stated in a way that makes it easy to answer and also with good intent. So much easier to answer things with good vibes attached to them instead of the bad vibes that for people like me are the wrong experiences. I literally spend all my time inside of the tuning vibe solving sound situations for people or having my mind in the right place while writing articles or evaluating. Getting out of tune is a drag and sometimes when I see people here on head trips or have bad intent it's simply a waste of time and productive life. thank you Glupson
MG