I have no in-line. I use a sidelock, and the trick I have used for years is to cover the cap with a piece of Handi Wrap. Enough to cover the cap and nipple, and let it cling around the base of that real good. The gun has always fired the cap with the plastic on. I also cover the end of the barrel with the plastic wrap, and then hold it in place with a small rubber band. Once I am out to the stand, I keep the cap area dry by setting some waterproof leather over that area, and if I have sat there for more then 4 hours, I replace the cap with a fresh one. So far, so good... It has always went off. I am not sure how you could apply this to an in-line unless you wrap the cap area... perhaps you can figure it out... Good luck hunting...