I just re-read this thread and some thoughts came to mind. First, I admire your tenacity and desire to master a flintlock.
I've hunted with percussion guns for about 30 years and I've had a few misfires with them. I had just about given up trying to kill a turkey. A deer 60 - 70 yards out doesn't always spook at the sound of a hammer falling on a misfire, but a turkey at 25 yards doesn't give you a second chance. However, I stuck with it, learned what was causing the occasional misfire, and corrected it.
I was never very interested in flintlocks because I'd heard they were less reliable than a cap lock and that the quality of the lock on most production guns was poor at best. I didn't think I wanted anything to do with a flint gun.
Three or four years ago I joined a muzzle loading gun club and begin to shoot in monthly matches. I discovered a wealth of expertise and experience existed within the membership of this club. Many of the members of the TMA also posses this same knowledge, experience, and willingness to share. But for me, seeing it is better than talking about it.
In any event, I have a neighbor and new best buddy who shoots in this club and hunts exclusively with flintlocks. He and the other flintlock shooters in the club have shown me that a flintlock properly loaded and cared for is very reliable. The most impressive demonstration of flintlock shooting I have ever witnessed took place at the Frozen Foot Rendezvous in 2011. It rained all day, all weekend. One of the rifle targets required shooting your rifle held upside down, above your head, and hitting the target. I don't remember how many shooters hit that target, but I do remember that every flintlock rifle went off without a single hang-fire or misfire. Upside down, and in the rain no less.
What I have learned by watching these guys is that flintlocks are no less reliable. They are just more involved than percussion guns. There are more items and details that have to be done right. I've also noticed that all these guys are shooting custom rifles with locks from makers with a reputation for quality.
I purchased my flintlock Chief's gun a few months ago with confidence in the builder and knowing I had the benefit of the expertise of flintlock masters to guide me through the learning curve. Without these guys to show me how, I would never have tried to learn to shoot a flintlock.
So far, I am getting along with my gun very well and it is becoming my favorite. But I know that if I have problems with it there are several experts right next to me who are more than willing to show me how to solve that issue.
You mentioned moisture and dampness in the priming. What I have been told is 4-f powder absorbs moisture faster than larger granulation. My friend loads and primes all his flintlocks with 3-f. When he hunts in damp weather or rain he keeps his vent plugged with a feather quill. Just before the shot he removes the feather, wipes the frizzen and pan with a dry cloth, and primes with 2-f powder. He says the 2-f powder is slower to absorb moisture and ignites just as easily if the lock is sparking properly. I don't know about all that, but I do know I've seen him shoot in a heavy rain with his rifle upside down and it worked fine.
This past June I attended the Texas State muzzle loading competition. Just down the line from me was a fellow shooting flintlocks and his guns had the fastest ignition of any flintlock shooter I have seen. I had a chance to visit with him and he was more than willing to share his knowledge with me. The most important thing I learned was that every flintlock has it's own particular variables. For instance, where the priming powder is placed in the pan can effect the speed of ignition. One lock fires faster if the powder is placed near the outside edge of the pan, another is faster with the powder placed in the center of the pan and another may perform best with the prime closer to the barrel.
I have been experimenting with my gun and some of these variables. I've learned that it ignites fastest with a prime of 4-f placed in the center of the pan. It also ignites faster with a load of 2-f than it does with a load of 3-f. I think I understand why this is so, but it may only be so for my particular gun.
I no longer believe flintlocks are less reliable than percussion guns. I have learned there are a lot more variables involved with loading and shooting flintlocks and the learning curve is tougher if you don't have someone to show you how it's done.
It's going to take some shooting and getting to know your flintlock before you get it all together. These guys here are a good resource but the best advice is to find a club or group of flintlock shooters who have already got it figured out. They will be more than happy to help out a new flintlock convert.