I need some help beating the materia keeper at Mt Nibel. I am using Cloud, Barret and Red who are level 27, 27, and 25 respectively as they are currently my strongest party members.

Here is what I've been doing so far;

Materia I have equipped includes Cure All, Ice2, Bolt2, Life, Enemy Skill (in order to get the 'Trine' enemy skill) and all the current summons. Magic doesn't really seem to do much so I've been hitting him with physical attacks and blasting him with limits. Odin is really the only worthwhile summon to use as most of the other summons only do as much as damage physical attacks so I save my MP for Cures.
I find that the most difficult part is when he uses Trine later in the battle which affects all party members but unfortunately I cannot use Cure All anymore. At the beginning of the battle I go well, but once he starts to cure himself and I run out of MP it's all over

Any tips would be appreciated,
Thanks...