The general idea of the code would be something like:
Build a list of 6 points, the corners of the bounding box of the ship.
Convert each of those point to screen space using Camera.main.WorldToScreenPoint.
Create a Rect whose parameters are (points[0].x, points[0].y, 0, 0). Then loop through each point and expand the rect to contain each one.
The rect will now contain a rect of the size you’re looking for.