When I previously made some I took inspiration from ….
USPTO patent applications submitted by and patents granted to Glenn Kuras
patents.justia.com
For the building of the frames etc
I have previous lined my diy record storage ( think Ikea but half as good and twice the price) with pool table felt(100%wool) off cuts from a billiard shop. I will use leftovers to cover traps in future.
I think the cheapest solution would be to buy multiple 2nd hand 100% wool blankets locally. Wash them fold them over and make them into absorbers. Frame them like above and cover them in wool of your choice. Either a dyed blanket ,felt or stretched merino fabric from fabric shop.
Unfortunately 100% wool blankets from the 60s and 70s have become trendy here. So it is cheaper for me to buy 100% wool insulation locally