Any recommendations please?
Ken.
Whichever one you choose, buy two, for when the first one burns out the element five minutes later. 
Waeco do a 24v kettle I’ve had mine 2 years now brilliant kettle
Iv never come across a good one and iv had a few over the years,
Always think them little camping stoves in the carry case and a small kettle are much quicker and easier to be honest
^^^ I personally would have recomended that as well, but the OP asked for 12v, still, …
It’s not for using in the truck, it’s for when I do road rally marshalling on a Saturday night, so a 24v is a no no, as is a gas stove.
Ken.
^ ah okay then Ken, sorry, can’t help you with that then.
Nah Ken, 12v kettles take an age to boil, and unless the wiring on the ciggy lighter socket are great, they usually burn the socket out after a few uses, sometimes the plug if the socket survives.
As all have advised, don’t! They all (12v & 24v) burn out very quickly and can damage your socket too!
As above, never had one that lasted and I’ve tried a few. I’d buy a flask and fill it before I left.
I bought a moonraker stainless steel 24v kettle a few months back as I forgot my gas stove, i was a bit sceptical to how long it would take to burn out, but so far (touch wood) its still going and takes about 5 minutes to boil.
I definitely wouldn’t recommend getting a 12v one as they are total ■■■■!!!