I was definitely planning on wrapping the entire structure in screen, not only to prevent stuff from getting in, but also as a medium for which to apply silicone.

As for the outside edges, I was going to push it against the back right wall so there was no gap. Then I was thinking of filling the gap of the front 2 open sides with aquarium rocks, topped with larger rocks. My thought was that the rocks would be a great filter, and would be easy to remove for complete cleaning.

Is this a bad idea because they will get stuck in there? Also, if I foam it in, is it permanent?

=rk