Wireless NAS for time machine back up

I want to set up a NAS over a wireless network to allow remote back up using time machine. The NAS needs to be raid 1 to improve data integrity.

I have a Lacie 2big network 2 connected by ethernet to a 5th generation airport extreme base station. When I connect the base station to my Imac i am able to back up usint time machine (first back up done over ethernet to speed it up, still took 5 hours) I now want to continue doing incremental backups wirelessly but can not see the NAS drive over my wireless network.

I am at the limits of my abilities so an answer aimed at a novice would be ideal.

Thanks in anticipation