I ran trotlines for crabs up in maryland. They have a lot less crabs up there in the chesapeake than we do down here so it makes sense to cover a huge area.. With that said.... its a good bit of work to do this. Personally it's to easy to catch a boat load of them down here in drop nets or handlines.
But if your still interested here is a link with detailed instruction on how to build one, how to set it, how to run it, and suggestions on what to use for bait.
http://www.bluecrab.info/crabbing/trotline.html
pm me if you get hung up on anything and need some advice.