DK Dungeon tanking?

Since there's always a lack of tanks at level 80 for rdf/rhdf (frostmourne realm), I want to play a dk tank. Solely for the purpose of running thru countless rdfs and rhdfs to gear myself up for a raid (in raids I want to play as a dps).
but I heard that dk tanks aren't viable in dungeons? is that true? and if no, what guide (spec, stat, rotations etc) would you recommend for dungeon tanking?

They're viable. Read Gnimo's guide for tanking on DK: http://forum.warmane.com/showthread.php?t=349830. You could use the extra AoE build he linked: https://wotlkdb.com/?talent#j0EMqIbf...t0MZ0gb:pioz0V
But tbh you could manage tanking with a default tank spec, just pop DND on every pull, apply diseases > pestilence > spam blood boil and rotate IT on every mob