It sounds like you're building a variation of the same system I built a few months back - have you considered using a food grade corn syrup container like the one pictured? I have two of them I bought on craigslist - they're 40"x48"x24" tall. I chopped the tops off at the second horizontal cross member down, fabbed lids using shower style paneling from Home Depot and 2" netpots, wrapped them in panda plastic so they're light proof, plumbed the manifolds about midway down in the root chamber, and plumbed the return lines to the built in spigots. I'm nearly 4 weeks into flower, and the growth I'm getting is truly insane. I have about 24" for roots before they hit the bottom, which they do.
I realize they're alot bigger, but just thought I'd throw it out there since it took me a couple weeks to find the right container for what I had in mind. They sit side by side under 2 600w lights.
Lastly, I second the remote res. recommendation. My res. is remote with nothing but my feed line through the top and between the feed / return / chiller / air / power lines - it is a real bitch to clean when I change my res, I can't even imagine if I had 24" of roots on multiple plants to deal with at the same time.