but the Fuel Rod BOBs are proving to be quite a challenge.
How so?
You spawn at the Spire with an Assault Rifle and DMR, so my trusty noob combo is just about out of the question. For the BOB that spawns closest to you, you can grab a Plasma Pistol provided Jorge doesn't scare him off. For the BOB that spawns far to the left, a direct assault is impractical, as he'll run one of three directions, and you can't catch up to him unless you happen to choose the right path. For the BOB that spawns by one of the Invasion generators, you basically need to Sprint up to him and pray he doesn't nail you with a Fuel Rod.
I think that for the far-left one you can come back and get him later when you've got a Banshee, I've done that before. The other two are likely to get spooked before you have a chance at that, so it's a lucky noob combo for the first one you see, and a desperate attempt at a Beat Down on the Invasion generator BOB. If you could push Jorge off the edge, it would be easier, but no luck.
On a related note, don't try to pull the fancy Assassination animation on these guys. They despawn 25 seconds from when they notice you; by the time you've caught up with them, you don't have time for the fancy stuff. I did a full no-death Legendary run, assassinated one of the BOBs, and THOUGHT that I got him. Watching the video, I saw that he despawned one or two frames from the end of the animation, and thus no kill. It's not the slow, gradual despawn of the Winter Contingency BOBs either, it's MUCH more rapid, which is an interesting difference.
If anyone has a reliable method, let me know. Running them over seems too risky; they just shoot you like mad as you slowly approach them.