I have same coolant block heater, about 1800w, I use a generator ,plug it for 30 min to warm up before start, because I don't have power plug in my parking place, most trucking companies keep them plugged here. Even so, and using synthetic oils, i had oil gushing around filters many times, i made 4 thick socks isolated and pull them on all 3 oil plus fuel filters during cold.
I read that, cold starts are first cause for engine failure here in Canada.