I saw this on the news but couldn't post it before others got to it. Yes, everything that has been published indicates that the Beast is a diesel - it makes sense as it's much easier to find diesel fuel, for example, at a US military base, as their trucks are all diesel. And it is built on a truck chassis.
Now, I do wonder what happened to the USSS agent who put gas in the tank. Ooops.
As for the tow truck, I guess, when you're abroad, you take what you can get...
Notice, the Presidential seals are off the doors.