There is an aquaponics site (using plants to filter fish water, nice symbiotic relationship) that I've seen that had lots on crawfish.
IIRC many used pieces of PVC on side to make holes/nests (BG type condo), some used stacks of them to give hiding spaces.
(looks for site-found it)

http://backyardaquaponics.com/forum/index.php

I can't do a search without logging in, but there was a lot of info on crawfish. Interesting discussions as it is based down-under, but has a world wide member ship.
Check it out, if you thought pond bosses were nuts, these people really take the cake.
I can't wait to try out some of the grow methods they use.
I keep eying the 220 outlet for the AC, it would run some nice lights and I keep seeing large (75+ gallon) fish tanks on Craigs list cheap, unfortunately the landlords live underneath me and I'm not sure I want to chance a leak of 50+ gallons of water down on them. I've had brand new tanks spring a leak after a month of use so they are out to get me, even if I am paranoid.

Matt