your HUD an previewer has to be on a layer with a parralax of 0, 0
so, it will not move with the scrolling
then, the preview vehicle Y position should be set to something like (Player.Y/Scaling_constant+Other_contant ), replace player by the name of your player sprite, for Scaling_constant, and Other constant, I cant really tell, I depends on multiple things...
Scaling constant is how many pixels your player should travel on the Y axis to make the preview vehicle move one pixel on the Y axis, and the Other constant is the position Y of the preview vehicle when you are at an Y of 0 yourself.
Sorry, I can't do that much, maybe someone can help you more