230V? 240V? I have this discussion with Trev quite a bit when I say "240V"
Always been 230v here in N Ireland, just tested it.
Trev, I will see your 230V and raise you 10V
This is pretty typical where I am. It very rarely ever drops below 240V and if it does only to 239V.
Back to the topic .... Electric Blankets
I used a full-sized one on my Safari Camperbus and it was fantastic. Used to use it off-grid no problem. I'd turn it on full on the journey and then on low overnight.
In the Motorhome I have the one in this link -
https://amzn.to/3eBz6LI - on the overcab bed (sized to allow me to still fold the mattress) and I find it very usable. Specs say 40W, but that is on full power, and you would not need to run on full for long. Run it on 240V/230V (240V EHU, or 230V Inverter

). Can you run off a battery? obviously depends on your setup and how long until you are driving again, but an overnighter? Absolutely.
I fitted it between the Original Mattress and the Mattress Topper so don't feel it all and the heat radiates into both and is retained nicely after it is switched down and then off.