Tape wasn't the only thing used... some enterprising ground-crew (and bomber gunners) would use extra prophylactics to cover gun barrel openings. The practice didn't last long though... trying to clean melted rubber off a gun barrel was not a lot of fun. And at high altitude the rubber would freeze and disintegrate.
That could also be construed as a word of warning for those considering admission to the "Mile High Club"... try it only in pressurized (and heated) aircraft!
Talking of which, I heard that British troops serving in Norway used condoms to prevent their Sten Guns freezing. As this only protected the muzzle, they requested that Durex (the major condom manufacturer in Britain) produce a version for them some 22 inches in length. When Churchill heard about this he agreed to give the go ahead under 2 conditions:
That each condom was to have 'Made in England' and also 'Medium Size' stamped on it.
S! Comp