If you follow our packaging guidelines, including 3/4" insulation and heat pack use as directed, shipping with a daytime high between 38F and 70F with a heat pack is safe and predictable. The overnight lows are relative to the daytime highs. You can see full temp and heat pack use guidelines here- https://www.shipyourreptiles.com/en/get-help/get-help-shipping-standards#question-275
I developed the temp guidelines myself, based on 20 years of live reptile shipping, and they are actually pretty conservative. I have shipped much colder (with some additional packaging considerations), but our goal with SYR guidelines is to give all shippers, experienced and new alike, the best chance for success.
Your package interior wouldn't be exposed to overnight lows in any normal expectation. Even the transport planes are pressurized and temp controlled between 55F and 75F.
And when you ship within our guidelines, you can also insure your live package for up to $10,000 on the site. If you want to discuss the temps for your specific package, feel free to call our SYR customer service staff, we are happy to answer questions, walk you through the process, and give you the confidence you need to ship safely and successfully.