The specifications book for the GLA posed two special challenges to the body engineers: the optionally available glass sunroof, far and away the largest in its class – 64 percent of the roof surface is glazed in order to provide the passengers in all seats an airy sense of spaciousness and the large tailgate opening to facilitate loading of the GLA.

Given the torsional stiffness of the body, to achieve the same high level as with a closed steel roof the roof bows in this area had to be adequately replaced. This was achieved with a double-skinned roof frame to support the B-pillars, an enlargement of the cross-section at the D-ring (the rearmost member of the body), the use of hot-shaped steels, and with an extremely sturdy glass sunroof frame firmly bolted to and bonded with the body structure.

For the wide tailgate opening, which enables easy loading even with bulky objects, the engineers developed a new body structure. Along with the usual D-ring an additional C-ring finds use. These two closed ring structures form an extremely stable unit and ensure excellent torsional stiffness. They also compensate for the loads generated by the new spindle-type actuator of the optionally available automatic tailgate. Very large forces occur there especially when automatic opening begins.

In addition, the two rear shock-absorber strut fixtures are supported by the C-ring. This decisively improves the resistance to forces transmitted from the rear axle connection and thus the NVH (noise, vibration, harshness) characteristics in general.

The GLA body confirmed the success of these measures during the severe marathon "track & field endurance test" over 80,000 km.