Since 1990 I have been riding with dogs....as far as Central America,Korea and Europe----2 Jack Russells, one Yorkie----2 died of old age, first Jack Russell-accident ran into boat prop in parking lot, when guy was running motor==quick death.
My wife and friend brought a new dog to me this week---looks like Jack Russell mix, 10-12 weeks old and I hope he stays small and so far good dog. I know there is Jack Russell in him---he farts and will eat poop if you do not watch him. He has practice sat in Hump Bag on SilverWing with engine running=ok. First road rides he will have tether to eye bolt on dash----later just sitting in bag--- he gets too big, I have GIVI box with Jack Russell size hole in top and some vent holes in sides and back...worked for several years and lots of miles. Planning on Chattanooga-Key West in Jan 2014, SilverWing, he goes with--name is Jake.
Dogs make long distance less boring and very handy for solo sleeping as watch dog/alarm.