Creating hiding spots for catfish using corners of tanks?

[biomechmonster]

I'm setting up a 180 gallon reef-ready tank. It will house four plecos.

The tank has two overflow boxes and each is about 7-8" from the side of the aquarium. I want to utilize the two nooks between the overflow boxes and aquarium sides and create a hiding place for the plecos here.

I was thinking getting two large half pieces of PVC pipe, siliconing some driftwood bark to the outside (to make it look natural) and putting the pieces in these nooks somehow but I don't want to silicone anything to the aquarium itself so I'm not sure how I would attach these makeshift pvc caves.

Any suggestions on how to go about doing this, or suggestions on other ways to utilize the nooks? I really see potential for them--they're large enough to house my biggest gibby comfortably yet small enough to make the pleco feel they're truly hidden.

[bronzefry]

I wonder if somehow attaching the pieces of PVC to a piece of slate would work? My curiosity would be about the bark of the driftwood. I see little Otos eating the outer bark like it's candy! Have you thought about somehow incorporating rocks? What are your thoughts? I love the size of the tank.....