I zoned in from Windurst Walls as BLU/THF 75 as i figured treasure hunter would help a little, started killing the Impish Bats & Mind/Fleshcravers near the zone. Called on my npc just after 2-3 battles just to make it go faster, got a key drop from one of the fleshcravers soon after, went and changed sub to nin for snk inv tools, then went back to get the coffer got it 2nd spawn place that i looked, all done in about an hour. Piece of cake.
Krawen
Asura
BLU75
MNK75