Actually, this "Fyrestone" map gives you at least one safe spot (I don't need more than that, obviously) where taking down the big toaster gets rather simple. I don't feel like making a video now (tried a screenshot, but I can't find a shot that clearly shows the position), so I'll try to describe it. You can use the original Fyrestone map to follow my directions; the DLC4 version looks pretty much the same.
If you stand where you start the game (after getting dropped of the bus) turn left and go to the southern fence (presumeably the bus CAME through there, although I have no idea why they nailed it shut afterwards). Follow the wall at the east. On your left, you will pass a large stone, then a small stone, then another large one. Then you'll get to the largest stone yet, with a path between that large one and a smaller one. Crouching in that "passage" behind the large rock will prevent the Kamikaze claptraps from reaching you, and the big bad can't do much either unless you stand up to take some shots at him.
Sorry, that's just the easy way of doing it. You can always do it the hard way, running around, taking care of the Kamikaze guys, trying dodge the big guns and nibbling them down. Presumeably that didn't work out for you, though -- playing a Siren, my own boss-combat techniques are of no help to you since you aren't phasewalking no matter how hard you try, so I'm not trying to give you soldier advice :-) My own soldier isn't that far yet, and he won't go open combat since he has a big sister that tells him where it's safe :-)