Under my 75 i only have room for the width and height of a 10 gallon sump, which is what I am using now. It is very cramped.. I do have more depth under the stand though. Does anyone make a tank that is no wider or taller then a 10g but deeper front to back?
I did a 29gl tank as a sump/refugium system. About ten years ago under my 75gl tank, until I got my 92 corner and bought a regular 75gl tank and made a sump/refugium system. That about 2 years ago and still run great.
Stang, this link shows the typical dimensions of a variety of tanks. It doesn't look like there are any other "wider" tanks with LxH dimensions that are similar to a 10 gallon tank (notice the shift in terminology... they use L where you might call it W). Anyway, the Rubbermaid container is a good idea or you could also pursue the construction of a DIY acrylic sump. I built mine for about 30$ in acrylic (it's on the order of a 10-gallon tank... actually works out to 15 gal) and is a custom fit for my stand. The only "special" tools I used were a table saw and a router... and it came out pretty good, if I do say so myself!