Its often convienient at the start of a session to have lots of mics ready to try ,
I often slip a mic wallet over , vinyl has textile backing , that may be prone to shed after a few years ,
A drawstring coin pouch or medicine bag might be another possibillity , with a non shed lining and a pocket to place the silica in , it doubles as safe storage inside the box during transport .
In a tube mic the internally generated heat might be enough to drive off any moisture from the silica while the mic is powered with the cover on .
I recently made up an air tight tubular case for a low D whistle , standard domestic white PVC pipe cut to lenght , a blanking cap at one end and a threaded inspection cover at the far side ,
its very suitable to pencil mics or even narrow body LDC mics like the AKG using standard kitchen/bathroom fittings from the plumbing supplies ,its a tough durable material and a standard pipe cutter gives perfect results , care might need to be taken in the choice of adhesive to bond the pipe and fittings , with usual adhesive from the plumb shop smells tended to hang around a bit inside the sealed case .
Felt might be a useful non shedding material to try as a lining ,
I used a circle of thick leather at either end of the tube ,slightly wider than the diameter so it formed a bump stop against shocks and impacts ,it worked well , in the case of a mic that weighs several hundred grams another way of supporting it would need to be thought up .