I know the other comment sent you down the block heater rabbit hole but I'd like to propose an alternative to that. Oil comes with two viscosity ratings, and we all know the first number with the "w" designates the winter rating - as long as you're choosing the correct oil for the temperatures you're encountering, your oil is not going to become ineffective. It will be fine, especially if you allow it to warm up before driving.
What you want is a freeze plug, and this is why. First of all, the oil takes care of itself like I said before, so a block heater is not necessary, and if it were then all pickups would come with them from the factory. The reason they don't use block heaters is because the frost plug heater warming the coolant and the radiator is more beneficial to more components than a block heater is. Having a warm radiator means that as soon as you start the engine, the transmission is also able to begin warming itself immediately as it cycles cold transmission fluid through the cooler located inside the warmed radiator.
A much more effective use of your funds would be to pick up a battery blanket (unless you have an AGM battery), and maybe one of these if you want to get fancy and/or are lazy like I am
You could get something like this plug here. You use a hole saw to make an opening for the plug, screw it in (you may also want to seal around it) then connect an extension cord to the outside when you need it, and it gives you power outlets on the inside of the shed.
Hahaha what about putting one of these on the shed wall and running a cord to it? NOCO GCP2 15 Amp AC Port Plug, 125 Volt Power Inlet Socket, and Waterproof Electrical Outlet Receptacle Box with Dual 18-Inch Integrated Outdoor Extension Cords https://www.amazon.com/dp/B07TLNQ328/ref=cm_sw_r_apan_i_TJED1K33YQKBF1CXE0P6
Thanks, this is very helpful.
This is the pass through I was considering: https://www.amazon.com/NOCO-GCP2-18-Inch-Integrated-Extension/dp/B07TLNQ328/
But my preference is to keep it simple if possible, so wont complicate it with extra parts if not necessary.
It's one of these. Lets me plug in the female end of an extension cord which powers my block heater, an on-board battery charger, and two shore power outlets I have installed in the dash (primarily to run a dehumidifier in the truck when it sits for prolonged periods, keep it from molding). For longer term plug-ins I just unplug the block heater and let it power the battery charger and outlets.
I'm not sure batteries will cut it here. I have battery heated garments, they were $300 each for the pants and jacket, they last maybe 3-5 hours. Running a 12v heated blanket off your cigarette lighter socket would work but you'd risk running down your starter battery too low unless the engine is running in which case you may as well just use the cabin heater.
However you may have noticed many places have unprotected outdoor power outlets for powering cleaning and landscaping tools, or at the bases of trees in cities to power christmas lights. There also still exist some legacy EV chargers with standard wall outlets for electric motorcycles. If you can fit a weather proof male passthru to the outside of your car, you can plug it into one of these public sockets via an extension cord. Like hooking an RV up to shore power.
Then you have power inside the car you can run a full size electric blanket (or even space heater) off of, all night long. If you buy an EV badge for your car, you can tell anybody who asks why it's plugged in that it's a conversion.
I'd put a plug mounted to the box then use whatever power strip you want for the inside.
Edit: fixed link
If you run them in parallel it should be fine. Just run a https://www.amazon.com/dp/B07TLNQ328/ref=cm_sw_r_apan_i_HE9PF1BS40JBTVA86V4P
Someone else made a good point on that pass through that I didn't think about. It is not UL approved so while it looks very nice, no one has evaluated it for voltage and current claims and other safety related things. So maybe not a great choice.
However this one...
https://www.amazon.com/NOCO-GCP2-18-Inch-Integrated-Extension/dp/B07TLNQ328
claims to be UL approved.
Keep in mind these are two extension cords on the back side so they have to share the input current. Meaning the 15A rating is for the single input plug and therefore if you use both the outlets then you are still limited to 15A total, not 15A per outlet. Again you are only looking at about 3.33 amps per heater so you well under, but something to keep in mind if you are running other things off these during the warmer months.
https://smile.amazon.com/dp/B07TLNQ328/ref=cm_sw_r_cp_apa_fabc_HUH7FbD50VPSR
Install this into the side of the van and plug the goal Zero into it. Bada boom
What r/secessus said. Super simple solution if you don't want to have window cracked or to pinch the cord by having it go through a door. https://www.amazon.com/dp/B07TLNQ328/ref=cm_sw_r_cp_apa_i_kjTnFb1ZW2QH2