Substitute transform.rotation + slerp with transform.rotate and Vector3

I am using this method, to rotate ship towards target:

     Vector3 pos = target.localPosition - transform.localPosition;
     Quaternion rotation = Quaternion.LookRotation(pos);
     transform.rotation = Quaternion.Slerp(transform.rotation, rotation, rotationalDamp * Time.deltaTime);

Yet for avoiding obstacles i cast numerous raycasts at different angles grouping them in directions[] array and use (for now simple method that doesn't average out the raycastOffset if there are 2 vectors at the same time, its not important now):

         raycastOffset = Vector3.zero;
         if(free_vectors==0)
             raycastOffset = Vector3.left + Vector3.down;
         else
         {
             if ((directions[1] == true)) raycastOffset += Vector3.left;
             if ((directions[2] == true) && (directions[1] == false)) raycastOffset += Vector3.right;
             if ((directions[2] == false) && (directions[1] == false)) raycastOffset += Vector3.left;

             if ((directions[3] == true)) raycastOffset += Vector3.down;
             if ((directions[4] == true) && (directions[3] == false)) raycastOffset += Vector3.up;
             if ((directions[4] == false) && (directions[3] == false)) raycastOffset += Vector3.down;
         }

[...]

     prev_raycastOffset = (prev_raycastOffset * (1f - (rotate_change_lag * Time.deltaTime))) + (raycastOffset * (rotate_change_lag * Time.deltaTime));
     transform.Rotate(prev_raycastOffset * rotate_speed * Time.deltaTime);

I interpolate the prev_raycastOffset, so that the ship has some drag (regulated by rotate_change_lag) while changing rotation to avoid obstacles. The problem is that when I look towards target with first function, it is clunky and I don't know how to merge these 2 methods (rotation+ Slerp) and transform.Rotate to include my rotation drag. Is it possible to convert the first function, so that it also uses transform.Rotate and an input Vector3 instead of transform.rotate? Then I could incorporate my one drag method for both types of rotations. Or maybe there is a better way?

I was thinking also about using Rigidbody and adding rotation force to achieve those rotations, which would give me much more natural rotation drag effect. It would be more professional, but I don't know even where to begin (not enough experience with it).