I've been running a Warden tank since Morrowind and have a few incites.
My bar set up:
Front - Leeching Vines, Polar Wind, Pierce Armor, Bull Netch, Ice Fortress, Healing Thicket.
Back - Wall of Elements, Gripping Shards, Inner Rage, Frozen Device, Deceptive Predator, War Horn.

Now let me explain my reasoning behind my choices
First is frost - with Wall, Gripping and Polar I have 3 frost AOE DOTs. This is important because of ices secondary effect, when you hit a Chilled target with a frost ability they become immobilized (Wardens talons) The second part is frost primary effect, Minor Main (AOE vs Low Slash 1 to 3 target).

Leeching Vines - Heals for getting attacked, but more importantly is the Nature's Gift passive, "When healing with a Green Balance ability gain x Magicka/Stamina. Restores your lowest pool" This is an amazing amount of sustain since 3 to 10 other people will be getting heals from you.

Healing Thicket - An oh **** skill, and 2% healing just for being slotted (Of course the goal is to save for War Horns)

Bull Netch - Free Major Brutality and Major Sorcery, Between the Netch and Nature's Gift block tanking is still easily maintainable. (Also can spam cast it to proc Engine Guardian, though I prefer Ice Heart (4)/Blood Spawn (12)

Deceptive Predator - Major Expedition and Minor Evasion, a mobile tank is good thing and I run Hist Bark so Major and Minor Evasion.

Frozen Device - This is the Wardens chains only better, it can be cast through whatever is in front of you, enemies, pets, players (tradeoff is the slight delay before its active).

Last piece is understanding the Ice Staff – Ice Staff is 30% block cost reduction and 20% additional damage blocked, 1H/S is 35% block cost and 20% additional block + 15% from ranged + 8% if you slot Defensive Posture. 1h/S the better “main tanking bar”

The Ice Staff Passive for Blocking is separate from the taunt/Magikca cost passive. Personally I don’t take the taunt passive. My blocking always cost stamina and the only other stamina cost is Pierce Armor, again feeding into maintaining Block Tanking option.

(My set choices: Hist Bark and Wyrd Tree (Magicka regen and only comes together on my 1H/S.) Monster set; Ice Heart/Blood Spawn/Troll King.

IMO Wardens are as good if not better tanking class than DKs, they just take a little more finesse. Give the build a try.