That ought to work good. Put weight in the bottom, more than you think you need. Large CC will move stuff around if it is near floating. I have had plastic stuff weighted down with gravel and had CC or snagging it with a hook move it around enough to lose its ballast and it floats to the top and wind blows to the shore.
The more holes for water circulation the better. Something that works really well for smaller holes is a step drill. Harbor Freight sells them pretty reasonable and the quality is fine for drilling plastic. They make a set of smaller ones that are too small but the larger individual (IIRC 1 3/8") work really well. Makes holes to the size you want in steps really fast and does not snag like a straight drill bit going through.
Step drill 
