Personally I never use auto car washes. They do a good job of putting loads of fine swirl marks all over your paintwork. They don't get all the dirt off and never clean the wheels properly either.
The chances of the little gps aerial on the Lag getting damaged are pretty slim though as it is a small aerial. A standard radio aerial is a different matter.
Also if you don't already do so, park the wipers in the upright position and fold your mirrors in. Less likely to damage the mirrors and the wiper arms are less likely to get bent. If your wipers judder across the windscreen even though you have new blades and a clean,grease,wax free screen, chances are the arms are bent slightly from using an auto car wash.