That's a sweet setup there. This is almost identical to what I did with a 60g under my 120. I lucked out and had enough room to fit it and a top-off container under it (60"W tank). Check out the GoodWill near you for a tank to use as a sump. Picked mine up for less than $20 if I remember right, and another $25-30 for the cut glass and silicone.
+1 on doing it outside!
Here's my setup. I know, its a mess under there....
View attachment 34426
+1 on doing it outside!
Here's my setup. I know, its a mess under there....
View attachment 34426