Well my group goes with the same healer set up, we not as well geared as you but good players none the less
and we are allways at 20-25% mana or less when we get to Halfuss we don't have any problems to keep the tank(s) up on him in that phase bare in mind that he don't do that much dmg on the tanks when all the drake's are down.
But if you are having truoble with keeping the tank alive, you should might consider switching the druid healer out in that fight with an other pala or maby a sham to help out the heal (since druid's aint the best healer class atm
)