Refugium vs. Return Section

[trwells]

I'm working on setting up my sump and after determining the size of the skimmer compartment I have remaining dimensions of 17inches in length 12 inches wide and 18 inches tall. The baffle coming out of the skimmer section is 11 inches tall to split between a return and refugium. The flow to the sump is split between the the skimmer on left and the refugium which will be on the right, with collection for return in the middle. I am wondering if anyone has any suggestions for what sizes to make the return and refugium sections such that evaporation won't be too much of an issue if I were to be away. I do not intend to implement an auto top off unit as of yet. My return is an eheim 1260 and the flow rate through the sump is about 360 gph.

Thanks

[ordy1]

skimmer on right, fuge in middle, return on left. Fuge and return combined. Fuge and return seperated by 4 inch high piece of acrylic to keep sand out of return pump. Glued eggcrate to 4 inch high acrylic.

http://i131.photobucket.com/albums/p288/ordy_03/DSC01832.jpg

Ordy