[Bones]

Personally I'd keep the res outside of the case for obvious reasons if possible. However you decide to set it up, be sure to have what is called "Drip Points" / low points in your tubing when you run your hoses. That means the tubing has a little dip in it as it goes to each fitting. Remember that water always runs downhill and these loops or dips use that effect to control where small leaks would go and drip off.

You can control where this is to make things more predictable once it's setup to help avoid disaster.
After setting it up, you could set another machine beside it or simply place a PSU unit (Not hooked up to the WC'ed PC itself) and run the pump to check for leaks before powering it up. Make sure when doing this, you do not have a power cord plugged into your WC'ed setup since dripping water from a leak could possibly short the circuits inside causing your WC'ed machine to try and start during this time = Uh-Oh.

When I first setup my machine, I simply placed another PC alongside the machine, hooked up one of it's PSU wires and ran the pump from this machine so it could run without having power going to the WC'ed machine itself.
By doing it this way, if it had a leak you'd have no power going to the WC'ed machine itself and be able to fix those without frying your setup. That is what I did and I found a few when I did that, fixed them and once my testing and fixing was done, hooked it all up proper and it did fine.