I'd give scrolls of Cure Moderate (either fudge the reading check or make up a reason why it isn't necessary (Heironean scrolls are all written the same way)) instead of potions. Potions are of very limited utility in a fight like this. As soon as the PCs pull out the potions, they're not attacking and the barbarian can just keep them guzzling the potions until they're out. (Not to mention, it provokes an AoO to retrieve or drink a potion so if the barbarian corners a PC, he's in a bad way). Scrolls, OTOH, the cleric can use from behind to heal whoever is being hurt. That way, the PCs main bashers don't need to take any breaks from putting the hurt on the barbarian in order to get healed.