Speaking of USB, you guys need to keep in mind that flash devices (i.e. USB thumb drives, iPod Nanos/Shuffles, most portable MP3 players, etc) are also prone to damage from shock. They are less prone than devices with conventional hard drives or optical drives, all of which have moving parts, whereas flash devices have none. But they are still vulnerable.
Over the long term your best bet is probably going to be a marine headunit. Also, never trust anything Crutchfield says; they constantly try to pawn off responsibility on defective items so that they don't have to RMA them.