The interior shot shows the Rock n Roller work room. This is where cars are serviced and stored when not in use. This area is within one of the main adjoining buildings.
It is not clear whether the cars shown here were supplied by Vekoma as test cars whilst the themed cars were still being delivered, or whether these cars were modified with new bodywork after this photo was taken. Please note that these cars are not the final cars! We also know that there are cars that are used for sand bag testing each morning before the ride opens, it is possible that these are those test cars.