six sided rectangle  with 2 ends open

the main sound deadner is this


https://www.homedepot.com/p/UltraTouch-48-in-x-6-ft-Radiant-Barrier-30000-11406/100656748


below for short proofing and fire resistant


https://www.amazon.com/Emergency-survival-Fiberglass-Blanket-fireplace/dp/B071744PRN/ref=sr_1_1_sspa?


if you build six feet long and 30 inches wide 1 foot tall  you can do 3 s-9's or 3 whatsminer m3's