My '48 is a daily driver and sits outside. We live in Tropical Montana but it can still get to 20 below or lower in the winter. I use 10W-30 all year round.
I have a frost plug heater (500 W, I think) under the intake manifold which is right where you want the heat. It's on a timer and on the coldest days, 4-5 hours is enough. It starts fast, idles well and warms up the defroster faster.
When it gets really cold, I also use a magnetic heater (250 W, I think) on the oil pan. I crawl under the truck to put it on but have a 2x2 with a hole drilled in it to pop the heater off in the morning (to help keep my clothes clean). I leave this heater on all night when it's really cold.
Here's a pic.
Oil Pan Heater. 
