So I thought I'd add my two cents because I got this pretty easily.
The first opportunity you have to face off against a bunch of bandits is during the first mission, right after Jill says they're holding off a bunch of 90 and you have to melee a pallet to proceed. This is also the same area you must stealth through for the
Unbreakable achievement.
Up to this point, if you've been keeping an eye out for materials at all, you should have enough materials to craft one molotov for a total of two when combined with the one you begin the DLC with. After continuing through the tunnel, you'll come across an area with a guy complaining it's cold with a school bus in the middle of the room. Directly to the right on a table when you enter is more crafting materials to make another molotov for a total of three. Continue forward and stealth kill the guy directly ahead of you, and the table has was standing at has more propellant to get you a total of 4 molotovs. Now all you need is the slightest bit of luck and/or skill to kill two guys with one of the molotovs.
What I decided to do was turn right directly from the table you collected the final propellant tank from and head onto the next platform. There will be an enemy wandering around there, and you want him to spot you just before you roast him. From the north, every other enemy in the area will file neatly toward you down the platform for some easy molotov kills. If you mess up, just restart the checkpoint.
Since this is also the area you must take no damage for another achievement, I recommend restarting from checkpoint to get that achievement done right afterward before you proceed with the campaign.