I do not have access to a squat rack either, and have been using the smith machine for squats for a little over 2 months with no ill side effects that I can identify.
I am training 5-3-1 - BBB, and my squat routine looks like this:
5-3-1 squats are done with a very wide stance, feet are more or less directly under me, toes pointing out close to 45 degrees.
For each of my following 5 sets of 10 reps, I narrow my stance slightly, move my feet slightly forward and close the toe angle.
My last set almost looks like the same position you'd be in doing a wall sit.
The only thing I noticed I needed to be careful of was making sure that as I narrowed my stance, I also moved my foot position further out in front. If I did not, my knees were traveling way too far in front of my feet and the next couple of days I would experience some slight knee irritation.
I am using split squats and step ups as alternate accessory exercises at times.
Good luck to you.