Rigidbody Velocity in Local Space?

To preface, I am making a 3D linear ship game, where the parent bounding box changes angles and position to move fluidly with the environment while the child Ship object can move within the X and Y local to the parent.

If the Ship within the bounding box collides with any object, I wanted to check to inverse the collision angle to move it further away from the object, however that requires Rigidbodies and Velocities, which I cannot seem to get working in Local Space as they only work in World Space. This is what I had for movement within Local Space prior to trying to implement Rigidbodies, though I know I'll have to change most of, if not all:

 float xPos = 0;
 float yPos = 0;
 
 //Check input, set vector speed
 if (Input.GetKey(KeyCode.W))
 {
     yPos = yPos + 1;
 }
 if (Input.GetKey(KeyCode.A))
 {
     xPos = xPos - 1;
 }
 if (Input.GetKey(KeyCode.S))
 {
     yPos = yPos - 1;
 }
 if (Input.GetKey(KeyCode.D))
 {
     xPos = xPos + 1;
 }
 
  //Set new position
 Vector3 newPosition = new Vector3(xPos, yPos, 0);
 transform.localPosition += newPosition * Time.deltaTime * speed;

Any help to get Rigidbody Velocities to work in Local Space would be greatly appreciated.