I have that case and use one of the lower two fan mounts along with the fan mount in the HD bay. I think your hard drives will live longer if you go ahead and move some air over them. Doesn't need to be anything drastic, just about any ol' 80mm will do. This case is so spacious, it's easy to keep cool.
My system temp reports ambient+1 degree all the time. I use:
two antec exhaust fans (they came with it)
Enermax EG-465P-VE PSU (which exhausts a lot of air)
two Sunon 30cfm intake fans (fairly quiet, but not the best)
one PCI slot fan to exhaust hot air from the Video card.
I don't think this much was really necessary. Probably one exhaust and one supply fan would be fine in this case but, I figure, the cooler I keep it, the longer it's gonna live.
I also use an Alpha 8045 HSF with a Sunon (40cfm) exhausting air away from the sink, which would tend to raise system temps, but this Antec setup just clears it right out. The case panel directly adjacent to the HSF doesn't get even a perceptable warm spot where the HSF blows at it.
Sidenote: The HD Bay will accommodate three drives, but be certain to use a fan if you do that because there will be little space for air circulation.