Cheap, drillable sump

[Delphinus]

Looks like a great option, should work well to keep salt creep at bay too.

One question though, is the back porthole the only access into the tank? The one drawback I maybe see is that inevitably you'll want to clean the inside of it or need to rescue a fish that rides the overflow waterslide, and it might be a bit of a hassle then? Unless there's another way in.