[BC Mosaic]

It really isn't that hard but i can see it being a bit intimidating. Use #16 Weldon (sp?). Its slightly thicker and doesn't set quite as fast.
I had the same project as yours. What I did is have spacers of plywood cut to the spacing size of your refugium. Use 2 pieces of ply. Where the ply butts up against the piece you are gluing down at the bottom cut out the right angle in that area of ply so the cynoacrylate does not wick or bond to the ply. Using 2 pieces like this, spaced apart, guarantees that the placement is square to the existing walls.

For the baffles, its the same thing but shorter pieces of ply (cut the bigger pieces of ply after you are done with them and remember the notch. This also applies if you were siliconing. The baffle that is raised to allow water to flow under, I cut 2 small pieces of the white PVC tubing and used them as support and to help set the height. These pieces should not touch the other 2baffles. The PVC should be at right angles to the piece, this way water will pass through them when you leave them there in place (i did).

I would also recommend that you fill each chamber one at a time and check for leaks. If you find one, empty, dry it out and reapply where necessary. This way if power goes out or whatever the water stays in its own compartment and doesn't mix with the water from the other chambers (refugium, skimmer,etc.).

Hope this helps