refuge design question

[Sasq40]

Im going to be having a 30g as a refuge for my 160, along with my 50 gallon sump, do i need any baffle in the fuge or can it be just a open tank? I will be ting of one return to feed it and it will be higher then my sump. Ill be drilling in and having it gravity drain into my sump, just so if there's a power outage there's no chance of overflowing