Completed beds. 20 mil liner and bulkheads installed. Ready for final pluming. The trough width is too wide for the standard blue foam (too much sunlight gets through and will most likely result in algae growth. My solution is to cut 2" PVC in half down the length of the pipe, attaching each half to a side. It makes for easy removal of my 2' x 4' segments, blocks the sun, is non toxic, and low cost.