Because motorcycles, have a Gerbing heated jacket liner.
Ran an extension cord from the 12V SAE plug we use for the trickle charger, and bought an adapter cable SAE -> Coax.
This one comes with an integrated controller: Olympia 12V North Bay Heated Jacket Liner - RevZilla
Adapter: Hotwired SAE DC Adapter - RevZilla
You can also buy heated motorcycle or snowmobile gloves. There are connectors in the sleeves.
They work great. The technology was developed in WWII for bomber crewmen.
As I mentioned in an earlier post, The coveralls are great as well... Depending on how warm you want or need to be. I used a smallish rechargeable battery I tucked into a pocket with mine when I was out in the property doing stuff. If I got cold Id flip a little switch I rigged into it, warm up and turn it back off ( especially the gloves, fingers get cold easily ) but its nice to be able to stay comfortable.