I wouldn't worry about the DEF consumption unless you are burning it up like crazy. I never stock up on DEF because it ages, there are dates on containes of DEF. My 2018 with 3.0 gave you a notice on the dashboard that you had 500 miles left before your DEF was empty, if you stopped the engine and started up again it would show the message.Wow lot better than I expected trucks at work seem to a bit over a gallon for every thousand miles.
Much appreciated
I wouldn't worry about the DEF consumption unless you are burning it up like crazy. I never stock up on DEF because it ages, there are dates on containes of DEF. My 2018 with 3.0 gave you a notice on the dashboard that you had 500 miles left before your DEF was empty, if you stopped the engine and started up again it would show the message.