Vehicles of any kind be it luxury trucks, sedans or otherwise may be fitted with armor plating in order to make them more resistant to small arms fire.
Narcotanks, as they have become known are a fearsome breed of Cártel innovation which are intended to be resistant to explosions and nearly impervious to small arms fire. They are typically adorned with portholes for rifles to shoot through, spare tires, bulletproof glass and sometimes even attached turrets where heavy machine guns can be equipped.
They are often reserved for direct confrontations and are kept hidden away in storage until needed.
These weapons of war were first introduced by Los Zetas under the leadership of Heriberto Lazcano Lazcano (El Z-3), whose forces utilized them against the Cártel del Golfo and other enemies in the early 2010's. Los Zetas subsequently gained notoriety for being specialists in the development and creation of these monstrosities - which are known aptly as Mounstros by the criminals.
Since that time, several criminal organizations have begun developing these vehicles in conjunction with the Z; but they are not as prevalent in use as they once were.
The practice of creating imitation police & military vehicles has become increasingly common among organized crime groups in Mexico. When the real thing is not available to them, fakes will allow members to easily pull others over. Be them innocents or rivals, making for swift abductions.
Perhaps more common than anything else we have utility vehicles. SUV's like the Tahoe, Escalade and Avalanche have become famous among the Narcos. Luxury trucks are extremely popular as well, and can frequently be found roaming in large convoys.
These vehicles serve many purposes. They are large and thus intimidating, and they are multi functional. Able to house drugs, personnel, weapons and victims. These sort of large convoys of big, intimidating vehicles were especially popular in the early 2000's and 2010's. However, police pressure on certain groups has caused some criminal cells to resort to much smaller, swifter and less conspicuous vehicles like the Volkswagen Jetta.