Or consider that Ferrari FXX has rims which are 85% magnesium, or that a Porsche Carrera GT has a transmission case made from magnesium. Both are exposed to the elements (The Porsche's transmission is directly under an exposed vent) and both handle it just fine.
As to the original poster, still...
1) Make the bottom perfectly flat.
2) Make the body a smooth curve from front to back.
3) Make a slight curvature from the sides to the roof.
4) Just generally avoid hard points, or any angles beyond forty-five degrees.
If you're asking from a dedicated performance perspective, I know that some of the drag teams I race run centrifugal superchargers capped at 40psi, but then over-driven several times so that they reach that boost sooner. Because centrifugals are more-or-less based upon turbocharger technology...
