No surface rust.
For starters - a blasted surface is very porous, the metal finished body of the Challenger is not. The body is very smooth which you can see in the pictures (sheen). We spent a couple hours going over the car with a scotch brite pad before the show to remove finger prints from the last show in March 08. Move in was hell, got caught in the rain, and ended up going over it again at the show.
Also - We get a lot of rain (Pacific Northwest), but it's not humid here. Our shop is also heated and well insulated - stays very dry. The car was on the frame fixture, uncovered, for many months.
Regardless - the chassis and inner body stucture will be powder coated, and the exterior will go through the proper steps for paint.