The cooler the better, the dryer the better, the fewest fluctuations in a month the better. Factors include the age of the tape, the conditions under which they have been stored, what shape they are in, the value of the tapes, the time frame of their likely usefulness in the future and the requirements for records retention purposes. Some sort of protection for the cassettes would be a good idea. Protection from dirt and dust, physical damage and particularly water. If the room or building they are stored in has a water sprinkler system, some type of protection is very important.
Most video cassettes are in plastic cases.
Adding a plastic bag would be OK if the tapes are pre-conditioned before closing the bag. Pre-conditioning is making sure the tape is nice and dry before sealing the bag. This is done by leaving the tapes in a dry area for a few days or weeks. Silica gel bags can be inserted into the bags to absorb moisture as well. Most film and tape archives do not use bags around video tape.