Bed warmers (or blanket warmers) are one option for keeping warm that is about halfway between an electric blanket and a space heater. It is a specialized heater that sits next to your bed and has an air duct that is placed under your blanket (or into your sleeping bag) to quickly warm up your bed with a dry heat. Bed warmers blow hot air into your bed and can make it toasty in just a few minutes. They can be a great option for nomads who have enough power and want to add more heating options and increase comfort at night. Even a very cold bed in an unheated van can be warmed up in 30 minutes.
Bed warmers are resistance heaters, so they will use 600-800 watts. This is significantly less than a large space heater, but it is still a pretty significant draw. For off-grid use, you'll need a robust electrical system capable of handling the load. Due to the nature of this appliance however, you will generally not need to run it for long periods, since you are only heating your bed instead of your entire vehicle.