Try witholding food for a few hours before the ride, then offer just small amts, at first when you reach the cottage. I used to have a homepathic rememdy which calmed them just enough to reduce stress, but I cannot remember the name of it. YOur vet should be able to help, but I don't know if they'd recommend dosing every w/end.Also, read Aine's recent thread, in the past week or two, "Moving my pussies" it should give some idea of keeping them comfortable in their carriers, etc.
Good luck,
kat