Freezing Starter?

Freezing should be fine.

As I understand it, it does not need holes to breathe in the normal sense. Anything that makes lactic/acetic acids or alcohols is not breathing oxygen, but it will breathe out carbon dioxide. Not that a starter won't use oxygen if it is handy, it just shouldn't need it. So it is not so much a matter of supplying air as letting carbon dioxide escape so the container doesn't burst. Quite a small hole should be good for this.

If you are taking it with you, I suggest you feed it generously and make it into a firm dough, and gladwrap it loosely. Chill it until you leave to give you a headstart while you travel.

Also, you can dry it. Just feed it and then spread on some baking paper (which I like to cover with a thick layer of flour) and leave it for a few days. When it is mostly dry, break it up to let the bottom dry out properly. It keeps for ages like this, and is handy to have in reserve if you like a particular starter.

I agree with Jem and would certainly make a firm dough with it before freezing.  If there is too much water present the water crystals can freeze inside the bacteria and yeast cells rupturing them and killing them.  The firmer the dough (ie the less water) the less likely this will happen.  I would then put it perhaps in a plastic bag so the bag is snug around the dough, leaving the opening ever so slightly loose until the dough is frozen (to let CO2 escape) and then once solid like a rock, seal the bag up tight and snug against the dough so ice doesn't form between the dough and the bag.  Done!

I never frozen my starter, but as a microbiologist, that is what we do if having to freeze unmentionable specimens at work :o)

Good luck! Do let us know how it goes.

Also, to minimize ice crystals further, be sure to refrigerate the starter before putting it in the freezer.