Be careful about drilling the bottom - many/most are tempered. Oceanic tempers their bottoms after drilling the holes.

I like Cliff's idea on the Calfo. As for your bottom drains, what I did on mine is put 3 strainers on each of mine - about 5" apart, about 5" above the bottom sandbed. It's been running that way for a year an a half, with no problems. With the drainage spread of 3 strainers on each return, I have had NO problems with anything getting stuck to them.