I missed that bit about flaming skin, so sad! lol. Well it still wouldn't hurt to stack fire resistance for an undead geomancer since your stuff is so flammable, flaming skin could just be saved for those emergencies where you've managed to set most of the area on fire but you'd rather not douse it out but instead just keep spamming your poison and oil skills. You'd benefit quite a bit from elemental affinity if you were able to stand in the middle of your mayhem too.
