Speaking as a Prot Paladin myself, I used Losie's post in this very forum.
Basically, it goes like this:
1). Tempered Titansteel Helm (or, Tempered Saronite Helm first until you get the money)
2). Tempered Titansteel Shoulders
3). Tempered Saronite Body (until you can use Wyrmrest's. Kalu'ak also has one)
4). Daunting Legs
5). Daunting Hands
6). Titansteel Shield Wall (you could start with the Saronite shield, but it isn't anywhere near as good).
7). Hammer of Mourning (easy 3-man Zul'drak quest that you can SOLO at Lv80 as a Prot Paladin wearing the rest of this gear).
8). BoE Cape (I used Tattered Castle Drape, if you got lots of Wyrmrest Rep, you can use their cape (and body too!)
9). Tempered Saronite Boots
10). Tempered Saronite Belt (don't forget the belt buckle!)
11). Betrayer's Choker (easy easy quest in Zul'drak once you learn the fight mechanics, you can solo this easy).
Add BoE Rings with +Defense Rating, or Stam/Str, whatever.
Keep in mind, you don't need 540 Def if you're doing just Heroics, 540Def is to be crit immune against SKULL Enemies. There are no Skulls in Heroics, only 82s. Slightly less than 540 is fine. (I forget the exact number for CI against 82).
TRINKETS are what the BIG problem is.
I used (and am STILL using!) Netherwing Commander's Badge (+45 Stamina, meh), and I got lucky and got the drop from Heroic Magister's. H-MgT should be easy easy easy for a Lv80 tank, even if he's wearing blues. Heck, I can solo some of the mob packs there, and I once 3-manned H-MgT.
Basically, grab anything with +Stamina. +Avoidances or +Defense Rating is really icing on the cake. You can try getting Karazhan pickups and pray for Moroes' watch to drop, or, buy something from G'eras (the Naaru in Shatt, who wants Lv70 badges of justice) that has Stamina, Defense, or Avoidances on it instead.
Once you get this stuff, look for:
1). Teldrassil Protector (Champion Rank with the Argent Tournament. Easy Easy Easy to get).
2). Wyrmrest Accord to Revered: You get a Cape and a Body out of this.
3). Argent Crusade to Revered: Head Enchant.
4). Sons of Hodir, Revered/Exalted: Lesser, and Greater Shoulder Enchants.
5). Kirin Tor to Exalted: Fireproven Gauntlets.
While you're doing that, work on...
1). Normal Halls of Lightning for Loken's Trinket. Be prepared to do a lot of these. 5 times now, no drop for me.
2). Heroic AN for another Trinket, another boss drop.
3). Watch the AH for BoE Blues, I got a pair of Crusader's Square Pauldrons which were slightly better than Saronite.
4). Durable Nerubhide Cape: About 500G from the AH.
5). Waistguard of Living Iron (40 Emblems of Heroism).
If you're having problems surviving in instances, watch the dailies every day. Even if you don't have time for a dungeon run that day, if the daily is something easy (Keristrasza, Ingvar the Plunderer, etc), take it, and keep it in your quest log. You can complete it another day! You just can't accept another quest in that same day. There have been days when something horrible like Occulus was the daily and I had H-Nex on me and got my 2 Emblems! Woot. Sure beats Oculus. lol.
So basically, once you're Prot at Lv80 and got your BoEs:
1). Do the Argent Tournament Dailies until you reach Champion Rank and get 25 Seals for your Teldrassil Protector. You will get LOTS of Argent Crusade rep from this. Thank God you don't have to do Troll Patrol.
2). Do Sons of Hodir Dailies.
3). Any remaining dailies should go to either Fishing/Cooking (for Kirin Tor rep) or Wyrmrest Accord (3 dailies here).
Hope this advice helps!