There is an article in the current issue of 'Good Old Boat' http://www.goodoldboat.com/
that details a very salty little green house that could live atop your vessel. I saw it in a store last week and picked it up, all while thinking of this thread. I moved aboard 15 days ago; I've been thinking about planting some herbs... Unfortunately I'll have to put away the green thumb until things get settled, not to mention the wind has been favorable here in NY: we must sail as we are sailors!