I like the win 209 reloading primer as they seal better.
Covering the muzzle of the gun will not help if the pellets have already gathered moisture. The box they come in does not seal out moisture, if they set in the store and gather moisture then you have a problem. All the granulated powders have a seal so you at least start out with good powder.

I called a powder company up one time and asked why I was having problems getting their powder to work well in my gun. They asked what 209 primer I was using and told them Winchester. They told me that the Win 209 premiers were the coolest primers on the heat scale!!! They recommended either CCI mag or Federal mag primers for their powder.

I found this scale on the internet:

Muzzleloading Primers

Hottest

CCI 209 In-Line MZL...241 f.p.s.
Fusion 209 In-Line.....236 f.p.s.
Remington ML............234 f.p.s.
Winchester ML............228 f.p.s.

Mildest

Winchester Triple 7....191 f.p.s.

I changed to the hotter primers and haven't had any problems since. It goes bang overtime. Used it in my CVA Apex and nailed my first wall hanger this year.

You don't necessarily need to switch to BH209... you can use loose powder (T7, Pyrodex) with your current setup and have good success I'm sure.

FWIW, I use W209 primers in all of my rifles that shoot BH209 with ZERO issues.

Same here as well...