There simply won't be enough in one sheet to have a euro brace of 3/8" which is why I would greatly consider 1/4" just for the Euro bracing. But as Dusty suggested Euro bracing may not be required and that theory is again reinforced by using 3/8". But for piece of mind sake I still recommend it or at the least two 2" wide 3/8" strips running the length along the top. But we can cross that bridge when we get there. Billy Zs idea will definately help if for some reason you wanted to segregate your refugium, But with the inside baffles lower to help maintain a constant water level you will still get backflow as well as bubbles, bubbles, bubbles returned to the tank. There is simply no way around this unless you go with a totally separate refugium.
I wish I had a nickel for every miracle that you easily tricked me into. -Chris Robinson