If you've gotten to vezax you'll find out that most of the mana restore that worked on retail isn't working on Frostmourne. As a pally the only thing giving you mana is Divine Plea and Spiritual atonement talent. This is not enough especially since the ranged dps are getting 50-60k crits with the dps buff. So atm it is not at all viable for Paladin tank to tank this boss.
I'm trying to put together a set/build that can viably tank him. I'm going to try the following build out tonight and see how it goes.
talents and glyphs :
https://wotlkdb.com/?talent#sZV0tAbuMGsIufdEbMz0M:zLc
basically using 2/2 spiritual atonement and 5/5 benediction talents. Glyphs: Seal of Command, Spiritual Attunement, and Shield of Righteousness. If the Seal of Command glyph I think this build might just work, if it doesn't I see no hope for paladin tanks on this boss shy of wearing dps gear.
Edit: Glyph of Seal of command doesn't work either, seems Warmane "tweaking" has made prot paladins useless on this fight.
TLDR go holy or ret for this boss :(