I hate to say this, but there is something seriously wrong if you're needing to plug in at -5, or if you have to do 3 glow cycles at that temperature!As it was starting to get cold here in Canmore (below -5), I was having to do 3 glows in the morning and then it was still spluttering a little but it starts perfectly now with the block heater.
I'd check that your glow plugs are good, and your batteries as well.
I haven't had any heater installed yet, and I have started successfully down to -20 (haven't tried colder) and I don't start doing the multiple glow cycle thing until at least -10 to -15