I'd really advice you to use some frost resist gear, Boda. The healers will be taxed quite a bit already, so helping them is a good idea, especially at the first few attempts.
Do not forget to put an AP debuff on the boss too. It makes a huge difference.
I assume you mean Ony ring not trinket - its a decent ring for the armor, regardless of where you fall in the "FrR or no FrR" discussion. If you go buy another Sentinel's Winter Cloak for +20 FrR enchant, use the +25/+30 FrR ony ring & a +50 FrR resist flask you'll shave off average 30% of all damage - aura, chilled stacks, blistering cold & frost breath. The cost will be losing 225 armor from cloak enchant, 1300hp from Stoneblood flask & the stats on the Ony ring you get vs Ashen Band. If you dont get an Ony ring a 2nd 264 head w. the +FrR enchant replaces it just fine.
TBH the item I'd suggest you farm up is the 264 armor bracers from 10man Saurfang. That should be a nice increase on EH from the higher-stam 277 ones from Marrowgar. Trinket-wise, consider swapping your Key for an armor trinket - either Unidentifiable Organ, Petrified Twilight Scale (maybe even Glyph of Indomitability).
<aside>I've stayed out of the recent back-and-forth over my posts re: FrR since at first it seemed the discussion wasn't focused on the theorycraft but opinions which are infinitely fungible. In the end it seems we landed in a decent spot - resist+armor is a viable option for hard-hitting physical+elemental bosses; and reasonable people can disagree, without being disagreeable. I owe Martie a set of chardev or WoWhead profiles for the tank gear setup I described, which I will happily provide soonish when I get back to it. Lastly, felhoof hit the nail on the head w. his comments about optimizing for Halion - while I agree Sindy HM is no longer a challenging fight, like many other people I like to optimize even if its not needed, and my main interest was to see if the same strategy would help on Halion HM (which it seems to).</aside>