This is new info. I looked it up yesterday. In Frankfurt, in the downtown area, the cheapest, smallest car is USD $450 per month.
Then the very cheapest station wagon with a stick shift (Opel Astra) in downtown Frankfurt is USD $970 per MONTHS. But the Opel Astra is not even a camper! It is just rock hard a station wagon!
A camper would cost you a lot more! The cheapest van/camper (Volkswagen Caravelle) will cost you an arm and leg! USD $3,241 per month, i.e. USD $100+ per night! View
http://www.kemwel.com/car.cfm . And this is the cheapest price form one of the cheapest car rental companies in Germany,
http://www.kemwel.com !
Additionally, in my experience, there are lots of problems with sleeping in your vehicle! What do you do when you're in a camper in the middle of the night, in a strange city? Safety is an issue here. Harrassment is also a factor! Cops all over the world cannot stand it, if you don't go to a hotel, and are doing something creative! They will wake you up! They have harrassed me countless times! Exceptions are rest stops in the summer, but then rest stops are outside, not inside, cities, and you will have to commute back and forth!
How about convenience? How pleasant is it going to be to sleep in a cramped camper? How pleasant is it going to be NOT to be able to clean up when you wake up in the morning? Even if they do include a space heater with your rental, if you keep it on, and if there's no 2nd battery, it is going to drain your battery! And then you won't be able to start the engine!
And, YOU won't be able to get started either! In the morning, your frozen joints and shivering body will sap your desire and/or energies faster and more thoroughly than any hooker ever can!
I suggest you find a 50 or 60 Euro hotel, and you will STILL save $50 per day!
Sorry for the negatives, but, after sleeping for 20 years exclusively in both hotels, motels, and vehicles, I'm just being realistic here.
Mike