The easiest none permanent way I've found is camo vet wrap. Typically used to bandage horses legs it has no glue or sticky stuff on it. Its a tape that only sticks to itself and you can do up a gun in five minutes. At the end of the day take it off and if you care to re-use it again. Cost is less than $2 a roll. Generally I do the barrel and scope of my predator guns the night before I go out.