So I guess you don't soak or even rinse your regs after diving? That's what I use them for, and storage. No reason to allow small critters to make a home out of my first stages. If they did, can you imagine what would happen to their little ears when the reg is pressurized?
I put my regs on a tank (30 cu. ft.) that I have for just this purpose. Then I pressurize them and let them soak in the tub after each dive.
That's why I didn't see much use in the dust covers.
I should mention that I have 3 Dite Rite regs, the only come with a press on (not threaded) cap that only goes on to the non-threaded part of the DIN connection. I pulled those off, since they only got in the way when I was threading them into the tank valve.
I also have DIN Mk25/G250 regs for doubles. I don't have caps for those, and have never bought any.
The reason is because of how I clean them post dive.
That's my frame of reference for my previous opinion.
If I'm on a trip, I don't do anything to the regulators until the last day of the trip.
As has been previously mentioned, the use of the caps for the protection of the threads seems like a good idea. I had not thought of that before.
I have a couple of those Armor brand, double reg bags. They are always stored in those bags.
-Mitch