Flints & Humidity? (more frustration)

[Mr. 16 gauge]

O.K., I've done EVERYTHING that I can think of to get this stupid trade musket to spark reliably....I've been checking it periodically throughout the year, and every time I try it, I get a nice shower of sparks to the pan.
Took it out on Sunday to get some practice with it, and.....same old problem I've been having since I got it! I get one or two shots with the thing, and then it misfires (no sparks) or, if I'm "lucky", I'll get a flash in the pan.

I'm about ready to swear off flinters, sell the damn thing, and by a caplock shotgun.....I can make those go "BOOM" fairly reliably.

My question is: Most days I shoot in the summer end up being unbearably hot and humid.....will high humidity affect the sparking ability of a flint?