Matt, clearly you are knowledgeable in your field. However, I must inform you that AC RMS voltage is not 0.707 of peak to peak voltage. It is 0.707 of peak to ground voltage.
Therefore:
AC RMS = 120V
AC peak to ground = ~170V
AC peak to peak = ~340V
Or, as in your formula:
AC RMS = 24V
AC peak to ground = ~34V
AC peak to peak = ~68V
http://en.wikipedia.org/wiki/Root_mean_square
EZtech, I can tell by your caring for you customer's needs and attention to detail that you are a woman of great skill and knowlege, and have provided your customer a fine installation.