I'd be building a 2U rack PC, which is about the same size as a standard PC tower on the side. I'd hand pick everything in the system and build it myself - possibly with a liquid cooling system even - to make sure it was done in the best possible way. It would be mounted in a 4-6U rack with a 1U keyboard drawer and the flat monitor/mouse on top of the rack case. I'd only be lugging this around to local venues and peoples practice areas/houses to do location recording and what not when the need would arrise. I think I'm gonna give this a go in a little bit.
Sounds like fun, but don't say I didn't warn ya.
A 2U case is hardly the same size as a standard PC tower. Most standard cases are around 7.5" to 8" wide, over 4U wide. The main problem you'll encounter even with a 2U case is that the CPU won't have much airflow. If you go this route, I'd recommend underclocking the CPU to keep the heat down and reliability up. The last thing you want while you're recording is for the OS to hang. Liquid cooling is an interesting consideration, but I've never seen one that could fit inside a 2U case by a long shot. And how do they hold up to being moved around?
Before you order anything, take a careful look at the specs (size and weight). I assumed you'd be going 1U since there are very few 2U cases on the market that would fit in a manageable portable rack like an SKB. My shortest 2U cases are 22.5" deep which would just fit in the largest SKB, but that's a handfull in my opinion. If you must have a rack case, consider rack mounting a more traditional case which will be far shallower and lighter, provide better air flow, and probably save you a couple hundred bucks.
BTW - if you do go this route, check out a 1U LCD/KVM (or just LCD/Keyboard). They're a great space saver and it lets you tuck your monitor and keyboard out of sight and away from prying eyes or spilling beers when its not needed. Here's an example:
http://www.tripplite.com/products/product.cfm?productID=2872Good luck!
- Jason