I now use the exalt freak case for my inserts but I also have a set of ‘tool folders’ for my various barrels and I was using them for the freak inserts
The screenshots are not the ones I have, but are a rough guide. I think mine were from Toolstation or screw fix
Mine have lots of elastic loops on both sides (like the left side of the photo example) which work for inserts or barrels
An alternative I’ve seen some people use are shotgun cartridge pouches like this: