03 Bonneville SE 3.8L
162k miles

Back story:
Owned my Bonneville since 2013, got it with 120k miles. Living in northern MN I've had zero issues with it not starting even in -20 degree weather. Recently in another spell of cold weather, it dropped down to around -30 for a couple days and she
finally gave out and wouldn't start. Initially thought it was the battery so I went and got a new one. Still wouldn't start, took some fuel additives and starting fluid to get it running, ran fine for a 3 hr trip home afterward (still about -5 degree weather). After another week of driving with no issues to/from work and another 2 hr trip, temps dip into -20'* again and she wouldn't start. Took a night in a warm garage at a mechanic and she fired back up again (mechanic couldn't find anything that might be causing the issue. Another 2 hr drive back home, an oil change, and after 2 days she wont start again in about 5 degree temps even with additives and starting fluid.

Key points in my rambling:
Car runs great once it'* started, no stuttering or surging, all electronics work.
No loss of horsepower when driving.
No warning lights on.
alternator was tested and is good.
battery is brand new.
still cranks and turns over, and engine "coughs" on the first few cranks but wont start.

All this leads me to think gas is getting frozen/ clogged from moisture somewhere (fuel filter, gas lines?)

Current plan is to wait until tomorrow to try anything else since its supposed to get up into the 20'*. Hoping that some higher temps will help.
Any and all advice on what to try next appreciated.

Add a bottle or two of some gas line anti-freeze with water remover.
Ethanol fuels like to absorb moisture & chances are the water/ vapor is freezing causing start up issues.
Keeping the tank full in winter is a good idea as well.
Finding premium fuels that is non ethanol in winter is best, if it is available in your region.
Luckily here Chevron 94 octane in non ethanol, and readily available.

I agree that gas can be a contributor but I am running gas with ethanol in it for all mine and they start fine at -20F. These cars get used regularly though. Do not want ethanol if they sit.
How has the overall maintenance of the engine been? When were the plugs and wires last changed? How about air filter and PCV valve. Has the throttle body ever been removed and cleaned per this forum?