The bad thing about humidifiers and foggers is bacteria and mold. I'm not sure of the specifics but warm + moist = problems. So if you are going to do a humidifier, a room one would be best, but make sure you clean it out at least once a week with bleach. Also because hard water and stuff like that can complicate those things.

A good way is a spray bottle if you thoroughly spray the tank it'll raise the humidity.

What kind of snake? I'm assuming BP since this is in the section, but you may have more species and what not. So for me to give this next piece of advice for raising your humidity is going to depend on what type of bedding you use, how much and what types of snakes?