With an 18650, there isn't really a negative side- the whole outside of the battery is negative, apart from the prongs that meet the topcap which is positive.
So when you mention the wrap peeling at the negative side, what is actually happening is more negative is being exposed- this can lead to your mod easily shorting the negative to the positive.
Electrical tape can, in theory be used for patching a nick in the side of a battery until you are home to wrap it, but I wouldn't do it if it is at the bottom or top of the battery, or even really advise doing so.