A good place to start reading is
http://www.melevsreef.com/allmysumps.html
I find the pics a little hard to follow on the site.
I think its cause every thing's transparent.
Heres a basic diagram of the last sump i put together out of a 20G
It's built to a remora on the side.
In your case you could just remove that compartment and split the tank even down the middle.