Logun S16xs bottle cap

I know there are quite a few shooters that are members of the forum that also machine small parts. Do any of you make bottle/valve caps for the S16xs and plugs for the bottle threads? I’ve been using the S16xs in the field and I have noticed that the valve is very exposed when not attached to the gun and the opening on the gun could easily get dirty. I’d really like to find a cap made of steel/brass and a plug made of some sort of synthetic material. Any advice is greatly appreciated.