I live in Alaska and it does rain here from time to time. I have been taping my barrel ends for decades and have not noted any decrement in accuracy but I tape my barrels differently from most. Most often I see people just place a strip of tape across the muzzle. In my experience more often than not as one makes their way thru the dense alders the barrel end rubs on the alder branches and after a while will have the tape stripped off. I clean the muzzleloader crown as best as I can (degrease is best), then I press the tape over the end of the barrel. Next, with a sharp knife I closely trim away the excess tape so that what is left is just a circle of tape that ends at the crown barrel junction and will not be rubbed off as the barrel end deflects off branches, under brush, etc. I do not use finger cots or anything similar as they can be rubbed off and many times when I have taken them off the next day I find some unwelcome rust. Since most of my mountain rifles have muzzle brakes the break openings also get taped. I have heard of hunters using foam ear plugs in muzzle end for protection from rain and snow but have no experience with this option -but seem like it might work well.