I have had Water Sprites shipped from Florida and Anubias from Louisana in the last 3 weeks. I live in Pennsylvania - and in particular, the days the Anubias were shipped, it was about 15 degrees out during the day. they all arrived safely no problems.
they weren't even sent in a styrofoam container - and no heatpack. Instead, they were in plastic bags with a little water (one had wet neswpaper wrapped around them in the bag itself), the bag was wrapped a bit in dry newspaper - and then this all went in a USPS Priority mail cardboard box.
now I was home to get them as the postman delivered them. You need to be there - can't have him just leave them outside when it is that cold.
BTW - the Anubias Nana and Coffeeolia were great plants - far bigger (12 leaves plus a baby plant on each one I bought growing) than my LFS ever would carry - for less cost