I simply use a foam hearing protection ear plug over the nipple. They are cheap and I keep two or three in my shooting bag just in case I lose one.
When hunting, I put a cap on and just set the hammer to half. But if there is rain or snow, I will put the ear plug over the cap and set the hammer fully down onto it. Dense enough to keep moisture out. If a shot opportunity happens, I can easily flick it off once the hammer is all the way back.
I often leave the rifle loaded between hunting days. I remove the cap and the ear plug goes over the nipple with the hammer down on it for that too. Helps to keep out moisture and the yellow ear plug makes a great visual indicator to remind me the rifle is already charged.
