I know it's tricky isn't it if it is going to take more than one day. Could you not set off really early - like 5am or something, get an early ferry and then do it all in one day - that way the hammies don't need an overnight stop. You could stop for breathers along the way and get there late at night or something? On the ferry, if the hammies are in pet carriers, you could take them with you to the passenger area rather than leave them in the car maybe - although maybe have to check on regulations on this - I once brought a plant back from France in a duffle bag and saw lots of signs saying no plants to be imported due to diseases! I was only 14 and freaked! Chucked the plant when I got to the Uk!
Just looked up the regulations for P&O ferries (link below) which say animals have to stay in the car. So I guess most ferry companies would say this. But Dover to Calais is only 90 minutes, so you could stay in the car with them for a bit maybe, and then come out for a breather and then go back and check on them now and then.
P&O Ferries Pet PoliciesE - Pet Travel
I can see what you mean - if it means two days and an overnight stop then it's a long time for disruption for them.
Whereabouts in Germany are you travelling to?
Just seen this - pet transportation company. They look quite good and also offer a service where they will drive you and your pet in a car and arrange pet friendly overnight stops.
http://www.pets2go2.co.uk/services/
There's also this company - they go by eurotunnel which is something I hadn't thought of - and as they say you can take your pet with you in the cabin on an aeroplane (and have a photo of someone with a guinea pig in a carrier on an aeroplane) have just checked that out too. They say if you fly they will drive you the rest of the way from Charles de Gaulle airport in France.
http://www.pet-moves.com/
Don't know how much all that would cost though. I checked out airlines and I think Air France are the only one that allow small pets to be carried in the cabin in a pet carrier - this includes hamsters. So I guess that's why the pet transport service say they will drive you from Charles de Gaulle airport. Their regulations are one pet per person though, so if you had two hamsters to transport you would probably need someone to travel with you.
It sounds like a great option - taking your hamsters on your knee in a pet carrier and then being picked up and driven to your destination by people who understand pets! But goodness knows how much it costs. Air France aren't the cheapest. But good old French eh?! They tend to have a more relaxed attitude about animals.
Here's the Air France pet policy. Look under 'pets allowed' - it says hamsters.
http://www.pettravel.com/airline_pet.../airfrance.cfm
I'm not sure though, whether a pressurised cabin would be ok? Anyone else know? I guess it would be ok for a short flight - it's only about an hour to Paris on a plane. I did notice somewhere it mentioned that cabin travel wasn't suitable for short nosed dogs who could get respiratory problems. But the fact they accept hamsters and there is no mention of any issues is positive.
Only thing is - sometimes it can be a long haul hanging around in airport terminals rather than just popping a pet carrier in a car and leaving it there for your journey - less upheaval.
If you did go by car and ferry or eurotunnel (with Eurotunnel you just stay in your car for the train journey) and couldn't do the journey in a day and needed an overnight stop you'd probably need a temporary cage to put up overnight and a wheel so the hammies could have their normal night time activity, but I think that would cause a bit of stress maybe, rather than going straight from one home to a new one.
Eurotunnel goes from Dover to Calais for cars I think.