Personally considering the cost of the guitars, the recording equipment and the importance of room reflection treatment,
I would just buy a nice finished product. For example:
https://www.atsacoustics.com/corner-bass-trap-b.html
P.S. I bought a portable room air purifier and ran it for a couple of week straight the day after I installed my rockwool wall and ceiling room panels (fiberglass would be even worse to breathe).