I like many things about he Barbarian class (using Maneha) but I don't like the concealment of Endurance while Frenzying.  My thoughts are that you use Frenzy to rapidly take out some opponents that you hope won't be able to take out your Barbarian.  So kind of different from a tank.

 

Another thought was to maybe use some consumables or scrolls or even tanky talents/abilities as 'insurance' that even though you don't know the endurance during Frenzy you still feel confident that the Barbarian will stay upright.

Agreed. Autopause low endurance helps

If you hover over your barb you can see that the color of the question mark (that replaces the number) changes. Green = higher than 75% endurance and so on until red = under 25%. That helps.

 

What also helps is stuff like Veteran's Recovery, Shod in Faith and Savage Defiance (which you can trigger once the question mark is red). Same as Second Whind. Also being Moon Godlike helps of course (since it triggers automatically at 75%, 50% and 25% endurance.