get sealable (e.g. ziploc) bags, put in a little bit of water, a lot of snails and loads of air. the air is most important, they just need enough water to cover them, then put them in a padded envelope and away you go.
hmmm yeah maybe if they're bigger snails, sorry was just thinking about when i've sent out mts's... sure the principal's the same but for apple's maybe a tub's better