Mogas or avgas

If using AVGAS, I’d certainly add https://www.aircraftspruce.com/catalog/appages/Decalin.php to strip out lead and make oil changes and tank cleaning easier.  It’s not nearly that cold here, so I can’t help with that.  Or why mogas would be more likely to freeze than avgas, you’d assume both are treated seasonally.  I try to run MOGAS almost exclusively.  No problems, although I do change my fuel filters mid-summer, just because MOGAS is so variable in quality.  I”d not hesitate to use either, frankly.  

The Mogas would be better in your cold environment and like Rick said use Decalin a lead scavenger to help reduce lead build up. 

Roger...no way.  Avgas has a RVP rating that is very low, making it very hard to start in cold weather.  Auto fuel is formulated for more volatility and much better in cold weather conditions. Auto fuel has double the volatility in winter blends. 

Cheers

Sory RW I meant 100LL Mogas. I typed the wrong word and failed to read it before posting. My mistake. I hate getting old. LOL

Gaston,

One trick is to put Avgaz in one tank and fresh (winter) Mogaz in the other.

. You takeoff  and land with Avgaz, that stays in the fuel system when not in use, and fly with Mogaz for the ‘cruise part’ of the flight. 
so, your Avgaz usage is minimal , but  still “protect” the system, having no ethanol in the ‘system’

if you don’t’t fly for  say 3 weeks, put the Mogaz in your car (if draining 1 tank is easy) 

my 2 cents