I've been getting good results with a slag conference call and an Unkempt Harold, dual wielded. None of the corrosives I've used have worked well on loaders, but I haven't tried my level 50 Hornet yet.
Something that does massive critical damage will help on constructors. They're immune to slag, if I'm not mistaken.
XBOX Live Gamertag: danishjuggler03 "I refuse to quote myself in my signature - I've always thought people who do that are lame." - danishjuggler21