Lower radiator hose heaters are good.
However, the MB instructions are clear, you don't want to crank the engine in short bursts. You should keep cranking it until the engine starts or the battery is dead. Multiple short bursts are counterproductive to starting in very cold temperatures.

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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