can use a dampit
can also use any one of a number of "in case" humifidiers. One
type is a ceramic cylinder that, once soaked in water, slowly releases
moisture. This type sits in your case.
humidifiers benefit not just your instrument but everything else in
your house that's sensitive to low humidity - including you! At
Tulsa Violin, we use the older model equivalent to these Kenmore
humidifiers, available from Sears. With these, we keep the
Shop's relative humidity no lower than 40%, even during the driest
stretches of winter.
your budget doesn't have room for any of these options, we have the
following suggestion: Buy the kind of soapdish that has two
pieces that lock together, making a little plastic box. Drill a
number of holes on one side to ventilate the soapdish. Soak and
wring out a sponge, put it inside the soapdish and secure the two
pieces of the soapdish together. This gives you low-dollar but
effective "in-case" humidifier that works just the same way as a dampit.