Automatic car washes are not safe for your car paintwork. The bristles will leave nasty swirl marks in your paint and may cause damage to wing mirrors and aerials. Self-service car washes are a better alternative, the pressure washer is usually quite powerful. It is important not to use the brush provided, as this will probably have been left on the ground and contain grit which will scratch your paint.
You could consider bringing your lidded buckets full of your wash solution and a rinse bucket. Some petrol stations may object to this, but if you go at an off-peak time you should not have any issues. Meguiar’s sell a bucket with a lid that will let you drive to the garage leak-free.