I use these to protect my air accessories. My ShoeBox, hoses and tanks. Little expensive but works well.
http://www.paintball-online.com/Custom-Products-Fill-Nipple-Dust-Cap-Protector-p/tkcpfndp.htm
http://www.paintball-online.com/Custom-Products-Fill-Nipple-Dust-Cap-Protector-p/tkcpfndp.htm