HI Andy,
If I was you I would read this thread (click on link below)and build you one of these. I have been using them on ponds for years and it catches crappies big time. I posted the instructions a few weeks ago but no one here has reported back ... yet. If you need any help just post any questions on that thread.
http://www.crappie.com/gr8vb3/showthread.php?t=19609