Curt
Look at your trees...with you knowledge of Crappie, how many will each hold???
Build cover for the fish, not for the fishermen....if you get your jig close to the cover they will come out to get it, you don't have to drop it in the middle of it...so don't make it to get lures back!
Crappie cover should mimic their Natural preference....make it dense, with as many large vertical posts as possible. Crappie use cover as protection, for rest, ambush points, and feeding stations.
When I build cover, I visualize how many 12 inch Crappie that I can HIDE in it!
I have areas with just stacked Milk-crates that hold hundreds of fish. Everyone has Milk-crates they want to get rid of...stack 3 or 4 together with plastic tie straps, big rock in the bottom. drop 15 or 20 in a tight group, and you have a tight stump field.
Bakeries/etc., will give away 5 gal buckets that sugar etc comes in....local concrete makers, give away broken blocks, bricks, etc. Lowes/etc., will sell broken 'crete bags, busted PVC etc....use the free stuff and build BIG!!!