I've currently got a 20XH set up, and am working on a 40B setup. I live in an apartment, and aside from the expense of insurance that would (supposedly) cover the expenses if one of those failed, I'd also like to avoid gifting my neighbors with water damage...
So, a while back (I can't remember where) I ran into some site that advocated taking a 4'x8' of plywood, screwing some edgewise 2x4s on the perimeter, and sealing the whole mess with epoxy. Claimed it should contain ~60 gallons.
I didn't have a lot of room for where I was sticking my 20XH (impulse buy, and all that...), so I went with ~2'x3', walled with 2x6, and used pvc shower pan liners instead of epoxy - no cure time, just used spray adhesive on the bottom and a staple gun uptop. made it in a night, and it should hold just about 17gallons, which is just about how much water I added to my tank after putting in hardscape and substrate.
Aside from the assurance I get from having a secondary containment, I've found it to be exceptionally enabling of my lazy impulses. After doing a water change, I just drop the hose right in the basin. same with anything wet, or any excess plants/plantparts that I pull out of the tank, yet can't be bothered with to do something else with meanwhile. And it catches almost all of the drippings associated with waterchanges and tank maintenance.
It's not something that would work for every setup, but where I have the tank is a fairly crowded space, so it's not really noticeable because there is so much other stuff around it.