I made one with a computer one time...it actually worked!
I like to toss out 4 or 5 of the circular ones with a small bait box centered in the middle so crawdads dont crawl around on the sides and chew on the bait. While those are soaking I toss out some danielson bait boxes designed for crab pots full of bait and tie them off and then net the crawdads when they start surrounding them.
Last year a couple of friends and I went out there and caught 250+ in a day... They were great.