If in fact you're on Kodiak, you're on the right track with the finger from a surgical glove. I've been using electrical tape for years because I can put it on without getting in the way of the sight. Does the same job though, which is mandatory in the rough terrain, mud, snow, rain and brush. The standard advice of keeping your muzzle down just hasn't experienced Kodiak. It only takes a single instance of trying to get a big plug of snow or mud out of your gun to break you of the muzzle-down habit once and for all.
Roundball's link and pointer is a goodun for the other end of the barrel. I've also used Chapstick, smearing a little on top of the cap, then rubbing it down the sides to seal. Even sitting out in the rain in a duck blind for hours, I've never experienced a misfire on my 12 gauge SxS using the Chapstick. Vaseline would probably work as well, but Chapstick is handier.
I use a cows knee on my flinters, but can't quite form the habit of using them on cappers, even though I should.