I use both flintlock or percussion as the mood strikes me.
I change the priming powder in the pan often, several times during a day's hunt. I put on a fresh percussion cap each morning, and if the day is very damp I might change the cap at some point during the day. However, I generally leave the main charge in my muzzleloaders for several days at a time during the open hunting seasons. The gun stays outside this whole time. I don't bring it inside to a warm room where a cold gun barrel will condense water vapor to trickle down and wet the powder. Leave it outside in your unheated vehicle, on a covered porch, or some such place.
I often hike into remote areas and camp under a tarp lean-to, not a tent. The gun spends the night lying beside me, but without a cap or priming powder. I have been out in those places for days in pouring rain and fierce blizzards. I've been hunting with muzzleloaders for over 20 years in such conditions, but I can recall only 3 times when they did not go off when I needed them. Once with a percussion gun, it was the cap that failed to fire. I put on another and the gun went off just fine with that one. The other two times were with a flintlock. One was a hang fire and although it did go off, it seemed to do so in slow motion. The other time I kept getting a flash in the pan, but the main charge wouldn't ignite. I had to pull that load.
Of course, in each of those cases, I missed the deer.