The fine, issued by the Government of Cantabria in March 2019 provided that during a routine check a weekly rest equal to or more than 45 hours was made in inside the vehicle.
The particularity of the case is that the driver previously took a regular 45-hour rest in Italy, without providing any evidence of staying in a hotel. Subsequently, in Spain, the driver was taking another weekly rest in the cabin, also exceeding 45 hours and without presenting evidence of staying in a hotel.
Since the new Spanish law came into force on 21/02/2019 you need to bear in mind:
Periods of time assigned as rest which do not meet all the requirements set out in the EC Regulations governing driving times and rest periods will not be counted as rest periods.
The rationale for this change, we understand, is that the Spanish authorities want to start controlling if drivers are taking their regular weekly rests of 45 hours in their cabins since under Article 8(8) of Regulation 561 this is not permitted.
Following this logic, if you are taking a regular weekly rest in the vehicle you are not complying with Regulation 561 and the period will not be counted as rest.
NOTE: General solution for all Europe
If you take two consecutive 45-hour regular rests, you will need to justify the two hotel stays. However, if you take a 45-hour break every two weeks in a hotel, you can take another break of up to 44h 59 in the cabin.