My opinion- All I can say is to try to set up on a cement floor next to a floor drain. If it were me I would close off both holes with screw capped bulkheads, drain the first reservoir to the height required by the skimmer (mod required) and drop an in-tank sump return pump in the second reservoir. That's my take. I don't worry about refugium because I have lots of critters living in my large shell Florida crushed coral plenum bed and live rock. Don't forget to size the skimmer first. Bigger is not better. Following spec is best. Try to keep the skimmer and return wet unless you are on cement next to a working floor drain.