I tried finding a farming route for thieves troves a while back and came up blank. What I finally did was when I DID find one I would take an alternate toon and park it at that same spot and so on and so on until I had 6 or 7 toons at various known locations and I just logged into each toon when I logged in for the day and then again when I logged out. I got the lead after about four days with little stress. I did that for the psjic portal lead in Southern Elsweyr they spawn at enchanting nodes so i just parked my toons at nodes. I do the same thing with some zone achievements when you have to "encounter" rare NPC's that can pop at many locations.