Space heater, electric blanket, or 4-season sleeping bag?

Why don't you just use your bunk heater like every other trucker on the road? You don't have to idle your truck to use your bunk heater.

 

My younger me, a few years ago. I used a sub zero sleeping bag.
N14 Motor treated fuel or idle the truck after 4 hours for 30 minutes to warm the motor.

DD 15 now, I have APU so I don't have to idle when it gets below freezing. I still carry sub zero bag for emergency.

Very important you get quality sleep.

 

Sleeping bag if you can stand waking up in a cold truck. Before I put my generator on the truck I carried a buddy heater and a 20lb propane tank. Didn’t care if it was legal or not. Rules end where my not freezing to death begins LOL.

But yes as 86scotty said, use the bunk heater and only idle when it’s really cold if you are worried about fuel issues.

 

My solution is a Webasto cab heater and I also use this LiTime 12V 200Ah LiFePO4 Lithium Battery, Build-in 100A BMS, 2560Wh En with a Cobra inverter. A timer is plugged into inverter and an extension cord goes to the block heater. The timer is set up to turn on every morning at 5.30am, so by the time I get up at 7.30 engine is already warmed up and fires up easily

 

As someone who has done the propane thing, be careful and don’t buy the cheapest. Little buddy rebranded but they have low oxygen shut off (in theory it won’t work on at high altitudes. )

I can’t stand getting up in the cold to start the truck. If you’re going to do the sleeping bag, a -20c or better mummy bag and a cheaper 0 bag around it makes it bearable to about -30c then you start adding layers to your sleep wear. But at -30 take your cell phone into the bag with you or it will be dead in the morning.

but yes best solution is a webasco or similar. I think an electric blanket may leave you short on cranking power in the morning.

 

Depending on truck, may have to have something preset/switched in truck.

With my last '18 Cascadia, I had to have either the foot well light or lower bunk floor light switched on for bunk heater to run.