With the upcoming changes to DK's Blood Tanks will more than be able to carry there own weight and will be contenders for the dk tanking crown. AOE will be much improved, mitigation in all specs will be better and Blood will have its own last stand talent.
Blood Tree -
***I'll let a Blood DK help you here ***
Frost Tree -
I see you want to pick up Lichborne, good move however by putting the 2 points in Black Ice (12%) you'll get more benefit than putting 2 points in Glacier Rot (10%)
Unholy Tree -
*** I'll let some unholy DKs help you here ***
Overall the spec seems pretty solid with a couple of small changes you are right on where you should be.