I use a couple 2.5lb BC rated fire extinguishers (One in cabin of truck, one in bed), you can get them at any target, walmart, meijer, etc. You would be surprised how quickly you go through them when you actually have a fire scenario
Ive had a fire in my engine bay before and its not so fun to cleanup afterwards either...
I have an ABC one at the base of my passenger seat. I’ve looked at those element ones as well but I’d personally rather have a full on extinguisher I think. I may or may not get a second one as a safety measure. Vehicle fires can go quick
*Ive had my truck on fire before (small engine bay fire from a bad electrical sheeth laying on the exhaust). You really do want 2 fire extinguishers if you want to be serious about it. I carry one in the bed of the truck and one in the interior...fires are scary when they are actually happening!