That's not a bad theory actually. If this is good and requires max campaign rank I'm going to be totally pissed since I'm the lowest rank. I swear, it's just not (or wouldn't be) right to offer little incentive for many people to even touch campaign, and then make some of the end rewards great. Recently I drafted up a 3-hit-setup for Dark Ixion using /RelicDaggerStage1, but the setup is kinda lame without Cobra Body. Thanks SE.
For Ermine's Tail you want to use Maze Tabula M03 (you want to resonate Great Warrior's earth element, and M02 doesn't have this), and at minimum you'll need Beast, Great Warrior, and Lost and Found. But it's essentially not worth doing this (or so I've heard--I don't really follow MMM too too closely) unless you also have Might and Supreme Might. Those increase the drop rate (dramatically?). So get them. You also don't really want to do this without a Job and Magic(ish) rune. Adding two more runes like Job and Magic (in magic's place, I hear you can add Force of Will just fine--you can probably add the rest of the stat/attribute and element related runes as well) probably increase drop rate further. But in the Dhalmel that drops Ermine's Tail's case, you want to give it Blm and Elemental Magic runes if possible. For those that don't know, this is because if you do this he tends to spend a lot of time casting spells and less time Healing Breezing (the major problem in the fight). So quick summary of optimal set: lost and found, great warrior, beast, might, supreme might, black mage, elemental magic.
With enough luck, doing this run is also profitable as Nefarious here made 900k+ that night in the space of about an hour, selling 2. Drop rate does seem to be ~1/8ish going from my ~40ish fights and from what I've heard from other people.
When we did that run with nefarious, our setup was:
Mnk, Thf, Thf, Blm, Rdm, Brd. March/Minuet I think (nice with 2 feint). I mainly played my dual-box red and Nef and the Mnk tanked. Don't need a Pld for the fight if the rest of the setup is correct. Replacing Mnk and Thf with Nin and Sam/Thf are also good. Don't need a Blm either, but the fastest way to take him down is with an SC (preferably with SA+ws's) and MB.