I do believe there are 24V versions of the heaters. If nothing else 24-12V converters the size you would need are really cheap. Personally though I hate using my vehicle battery for anything not related to starting the truck, so If it were mine I'd use an Orion converter as a battery charger for a 3rd battery and use that to power the heater.
There is a fuel pickup that is capped off that is used for the diesel heater in the ambulance version, so would be easy to just get fuel off of there. The heaters don't use huge amounts of fuel, so getting a small tank to run it off of would work, or make something using a 5 gallon fuel can.
You'd need to either mount the heater outside the cab, and have holes for input/return air lines, or you would need to mount it inside and make a hole with bulkhead fitting for the exhaust pipe.
Personally I wouldn't do any type of permanent mounting for it on my truck as I don't trust them to withstand that type of abuse.
I've used a self contained one a few times while camping (looks almost identical to the one you linked), powering it off a spare 12V deep cycle battery. The draw is pretty low, so the battery does last pretty well. I just set it on the ground next to my tent and run the output hose in through the zipper. In 50 degree or warmer it makes the tent too warm, even on it's lowest setting, so mostly use it to heat the tent for after my shower. (yes, I am more towards glamping than I am camping.)
btw, don't bother with the 8kw version. All the reviews I've seen show the same parts and fuel consumption as the 5kw version.