Ventilation slots on large helicopters can be found on the dome bells of the Bell 204 and Bell 205, both horizontally and vertically.
The air intake panels are usually made of metal and aerodynamically shaped. They ensure ventilation of the starter generators and the engine/turbine compartment.
To make sure your model is true to the original, glue these easily malleable ventilation slots in the appropriate size at the desired location on the fuselage with superglue before painting.