Thanks for the input. I'm going try a few different types of cover and see what I have the best luck with. The pvc cubes with tubing sound like a cool idea. Here is a pic of what I'm going to try first. I plan on putting four of these in one area.
I like it.
We've had good success with three types of "artificial structure" among the best for us has been large oak limbs cut then hauled to the lake bed when dry by tractor. Also, just simple two by fours sharpened on one end and driven straight into the bottom on about 18 inch centers in a square.
Another thing that has held bass well is three or more large tractor tires tied together in a pyramid.
Large concrete tiles, really big clay or terra cotta flower pots, piles of riprap, among other stuff works well.
For shallows, I'll fill the big (3' across) terra cotta pots with soil and plant taro (elephant ear), umbrella palm, or thalia for both relief from the bottom as well as a shoreline type island with shade in the shallows or on underwater humps.
I've also seen several commercial types of structures in use and they tend to work very well, especially in the absence of other structure or submerged aquatic plants.