Here is a snapshot of a couple spawning pads in the mob trap:
Built about 36 3x3 spawning pads from jungle leaves(pretty sure spiders can spawn on any leaves or on the ground but the leaves should cut down on other spawns)
Surrounded the pads with vine traps.
Enclosed the whole thing and made it pitch black.
I have not had one spider spawn yet. Many ocelots but no spiders.
I am currently working on clearing and lighting the surrounding area but I should have had at least one by now.
I have made sure to stay near enough for the chunk to stay loaded but far enough that I shouldn't effect the spawning.
I know that if I cross to the mainland and head into the jungle I will run into a spider within a couple minutes so I am not sure what I am doing wrong.
When I first built it I left the roof off to test it with access to the sky for a couple days and nights and didn't see any spiders.
I believe Battlecat is also having an issue with his trap as well.
Any hints would be greatly appreciated.