Our guild uses a pally/priest healer set up as well. Our WoL from our last Horridon kill is below:
http://worldoflogs.com/reports/rt-3r...m/healingDone/
As stated by Sonnillon, it's REALLY helpful to have assigned interrupts for door 2. It'll end up saving healers a ton of mana in fewer dispels and heals. If you end up 3-healing, I would suggest having each healer assigned to dispel their own group (so pally on group 1, druid on group 2). It makes the dispels more efficient and prevents dispels on the same person.
This is a pretty mana intensive fight until you learn the fight and execute it smoothly. Once you consistently down the 3rd door, you're in the final stretch and should be nearing a kill. The last phase is pretty easy but the tank will be tanking huge hits every once in a while. Make sure you have CDs (AW, Sacrifice) up and coordinate mana cooldowns so that there's never more than 1 healer inactive (Divine Plea with glyph, Hymn, etc.)