Although I have no idea about the origins of the rocker panels, I do know where ‘dashboard’ came from. Back in the days on carriages, they placed a board in front of the seats with a bar on it to put your feet on when the horses were dashing, and kicking up a lot of dirt and mud. As they moved to horseless carriages, they became a convenient place to put gauges and levers. The name just stuck. I think a few other parts names are probably similar.