Help! Rethinking sump

How about building a "side" compartment to hold electrical?

 

Take a look at the attached .

 

How about posting a picture or 2 of the setup?

 

A 20 gallon long is a bit small for a 90 gallon display. I wouldn't be worried about the refugium size necessarily, although it is a factor, but if you have 3 compartments, intake, refugium and return, the water level in your return area will lower very quickly due to the evaporation in your DT. Plus, the turnover rate through the sump will be much faster, probably too fast depending on your return pump. I had a 20 gal. long for a 55 and it worked, but I would want something bigger for a 90. If you want the electrical compartment, you're going to have to sacrifice something. Personally, I would use the 29 gal. You will clean the collection cup much more than the skimmer. In fact, the only reason I ever cleaned the body of my skimmer was to clean the pump every 3-4 months.