A little off-topic, but as you have done a pan, I assume it is a Beetle shell you are planning to sandblast. Whilst it would be ok to do the shuts/inner wings/unseen areas, sand blasting will distort 'open' panelwork. The metal will actually grow towards the side being blasted and can cause significant distortion.
Most folks state that it is the heat generated which warps the panel - it's one of those myths which just won't die, and is demonstrably incorrect as wet blasting makes the distortion far worse. The effect is as follows. Each particle of abrasive indents the surface, creating a jagged crater with the metal having been pushed out around the 'pit'. The millions (billions?) of tiny craters create compressive forces in the blasted skin of the steel, and the net effect of these forces trying to equalise is that the metal bulges towards the blasted surface. Peen forming or straightening and controlled peening for fatigue life works on exactly these principles and is an interesting and little-known subject worthy or research.