Adjusting Roll and Pitch with Velocity

I'd like the roll and pitch of my submarine to react to changing direction. Going back-and-forth changes the pitch; side-to-side changes the roll.

I have the following code that lerps between a x and z rotation as a function of x and z velocity

 xVelocity = rigidbody.velocity.x;
 yVelocity = rigidbody.velocity.y;
 zVelocity = rigidbody.velocity.z;
 
 maxXVelocityPercentage = Mathf.Abs(xVelocity / maxXVelocity);
 maxYVelocityPercentage = Mathf.Abs(yVelocity / maxYVelocity);
 maxZVelocityPercentage = Mathf.Abs(zVelocity / maxZVelocity);
 
 activeXAngle = Mathf.Lerp(0, maxXAngle, maxXVelocityPercentage);
 activeZAngle = Mathf.Lerp(0, maxZAngle, maxZVelocityPercentage);
 
 
 if (xVelocity > 0)
 activeXAngle = -activeXAngle;
 if (zVelocity > 0)
 activeZAngle = -activeZAngle;
 
 transform.localEulerAngles = new Vector3(activeZAngle, 0f, activeXAngle);

Works great when the sub is straight in the scene, however, if not, then the sub starts reading any movement as contributing towards the z velocity and giving me weird rotations.

Gif of the issue

Is there a way to localize velocity? Or a better way of doing what I'm trying to do?

Thanks!