Long Term Parking
There is no limit to the amount of time you can part at the Nantes Airport. You will of course pay but you'll be able to park as long as you like.
If you think you might be parking long term - for more than a month then an 'abonnement', a parking pass would be the cheapest way to go.
For example parking for two months in the cheapest car parks P0/P1 would be over 200 euros. But a three month airport parking pass would be about 150 euros.
The airport car park can be reached on 02 40 84 81 00. It's possible for the parking pass form to be sent through the mail.