Separating different sized rainbow trout

Here is the setup:

I've got 7 rainbow trout. Four are in a Rubbermaid 150 gallon stock tank ranging in size from 8-13 inches.

I've got three smaller fingerlings currently in a 10 gallon away from the bigger more aggressive trout. They are from 3-5".

I want to divide my 150 into two compartments so I move the three small trout to a bigger area.

I was wondering if egg crate plastic would work?

Any other ideas?

Thanks

Here is a pic of it from last fall (but the rocks are all gone. The cinder block is still there. The trout hide in it):

http://img.photobucket.com/albums/v615/Gambusia/Stock Tank/016_14.jpg