Tanking CM really doesn't require much gear at all. Starter 50 gear is fine for it. Just remember to rotate your cooldowns and make liberal use of your stun.

You'll have more trouble holding threat off your group members than you will with the amount of damage you're taking, and for that reason I suggest getting whomever you're paired with to take OT duty unless they're similarly inexperienced. Getting threat on half a dozen adds that are being AoE'ed down by the group is much harder than getting single target threat on a boss.

The only way damage gets out of hand is if you're playing sloppy and taking hits you don't want to take.