So I epically failed the first time and it looks like I ended up going the friendship gulag route. The problem is I still cant' beat the warden. I was at level 12 and I was getting absolutely no where, so I left the mission and went and did a few side missions. I am now level 14 and I have a rocket launcher that barely does 1000 damage, am I ready to face him?
While I can not answer your question directly, here's some advice.
Get a sniper rifle or an accurate launcher, and feel free to stay away from W4R-D3N, picking at his eye from afar (from the middle or from the left). This way you won't get swarmed by bots and will still kill it eventually.
EDIT: Considering W4R-D3N's shields, as well as obviously bringing shock weapons, one can use "speshul tactics" - when engaging Loaders, do not let constructor's shields go up by sparing a bullet every 5 seconds or so - you don't need to do any considerable damage, just register a hit. This is, of course, easier on a mouse...
AFAIK, all corrosive weapons can cause corrosive damage over time, if this is what you mean by "acid burn". They can be found aywhere. But do not think that corrosion is a must, an explosive or an accurate physical weapon will still do.
The WAR-D3N, like all Constructors, is crazy hard to kill unless you hit his eye. I noticed this while trying to kill Constructors with Corrosive DOT with an SMG. It took forever until I shot it in the eye a couple times...suddenly they were easy. Just shoot they eye; the problem is the eye is their crit spot, and everywhere else on their body is resistant to damage (even corrosive isn't great unless it hits the eye). I don't actually recommend using launchers against WAR-D3N, since they can't critical hit.
As far as level, you should be no more than 2 levels below WAR-D3N's level; the damage you and enemies take is scaled directly by level (there's no hidden stats, it's a %), so if you're 5 levels below WAR-D3N he'll deal insane damage to you, and vice-versa if you're over-leveled you'll easily slaughter him.