Guys there was a lot of thought and experience from Dodge on this, particularly for cold weather. The DEF tank is 8 gallons give or take a little. There is factory heating system in the DEF tank, and the DEF thaws at about the same rate as the engine warms up to running temp.
The DEF is only used for the regen
therefore the fluid is thawed by the time your exhaust temp would be anywhere near even a low level regen.
Chrysler also has heating elements in the fuel filter to prevent gelling in cold weather.
And ceramic glow plugs that are much faster to heat than traditional elements.
These rigs are not really limited by climate. If you get into consistent -30F or lower temperature you may have troubles thawing the DEF system and that is fixed like any gelled diesel, put it in a warm shop and let it thaw out. Clear the codes and go on your way.
The first 3D I ever drove it had been -25F or colder for the entire week (I am 10 minutes from the Canadian Border in Minnesota) and the truck had 10 miles on it from delivery and inspection. It hadn't ran since. The truck started with the remote start in the lot. No issue at all. And with the heating system for the fuel, it obviously works because I'm sure the new ram's don't come off the production line with straight #1 fuel and when it has a quarter tank to ship, (even if it were straight #1 the temps were close to gelling) so I trust in the system first without much question.
So 2 months later after watching and waiting for the 2016 model information considering waiting for the new production year to start. I undoubtedly ordered my LL 3D.