Switching to synthetic 5-40 should give you about 10 degrees lower starting ability. If you know you are going to be in severe cold with no access to electricity, carry a small gas generator if you have one to power the block heater for a couple of hours before starting.
But, one very important component of cold starting is to remember that your odds are always better of getting it started on the first attempt. Glow a couple of times, then hold the key in the start position until one or two cylinders start firing. Keep the key in the start position, helping it to run on a couple of cylinders until enough other cylinders jump in to keep it running.
If you stop before it starts the first time, the odds of getting it started on a second attempt are considerably lower.
The instructions about using the starter to keep it running on a few cylinders come directly from one of my MB manuals.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13