Oath shot is key for my build... without it, good luck.
As for where I farm, all I will say is it is in the desert.
My ranger's IGN is Sinthea Firebrand, if you want sometime perhaps I can take you on a crash course in solo trapping.
I've got over a million xp, and that's without trapping UW repeatedly - I never did get drops down there worth both the entry fee and the hassle of dealing with others.