You do even need the ND the regular would be fine. Few use the night drop feature.

Don't take this the wrong way but should you be looking at expanding when you are having trouble spending a few hundred bucks on the primary health and safety tool needed? It is like buying a car with no wheels and trying to save cash by attaching bicycle wheels. You get what you pay for, and IMO a fail safe t-stat is not really an optional item especially with a rack.