The best place to likely farm the Skins is Mount Qinkai (leaving from Breaker Hallow ), where i got about 1 Naga Skin per group, with 3 groups on the beach and then 2 in the lake above Breaker Hallow (that u will have to double back to btw).
You can SoS solo them rather than take heroes or henchmen, the trick here is just tactics, it includes the general "stick and move" associated with the SoS solo, however target the Warriors with Painful Bond first, and just as u r encountering them, they will advance first being melee and so ur spirits will actually attack them 1st, then they will attack the rit(s) as they have the lowest armor rating, saving the archers for last which is good since their elite is Escape and they can block ur spirits attacks, which is what makes this farm such a time consuming pain in the ass.
The exact Solo solo build i used as far as skills go was this:
>Painful Bond
>Vampirism
>Blood Song
>Shadowsong (important vs the Warriors and the Rangers)
>Signet of Spirits
>"Feel No Pain" (Norn skill)
>Armor of Unfeeling (necessary as with any SoS solo farm vs anything above level 10)
>Summon Spirits (using ur highest Luxon or Kurzick rank if u have the skill from both factions )
Btw, be sure to take advantage of the Luxon Priests Blessing (or Kurzick priest, as it is atm), even if u arent a Luxon (or if u are like me and its runned by kurz atm, take the kurz blessing.... fuck faction), it makes things easier, and that, along with "Feel No Pain" gives u a +6 health regen... which is none to shabby.
That's all, gl/hf
Atty