i've seen a few people use tanks that were quite tall and buried, but they don't allow the fish much swimming room imho.. but the only reason you need surface area is for oxygen transfer.. if you can pump air down 8', that wouldn't be a concern
the other problem with a "deep" tank would be that you could get a "thermocline", and in a water turnover, your temp could swing drastically and cause stress/fish deaths.. i don't think you'd have that problem with an 8' deep tank though
be kinda hard to catch the fish without a good net system too