I have still not done a water project in a mid-atx case. I keep telling myself that I need all that rad space, and now that I have everything under water, I'm rethinking my original mid-atx case. As you can see by my pics, I'm currently working in my full case, and there is all kinds of room.
If I had the money, I'd buy a caselabs bottom mount for just the rads...I just can't justify what they want for their cases...but they are sweet!
Seems that the old, veteran case-modders don't post much anymore.
I learned a lot with my bigger-than-full-tower 1995 Compaq ProLiant Server case-mod. One of the things I learned: you can make a lot of modifications with a minimum of sheet-metal work and consumption of time.
One thing I did: I put all my HAF midtower cases on two-inch braked double-caster wheels. [Look on the web for a place called Lawless Hardware.] I think it's less than a $20 investment. I get the units that have a square plate with four holes convenient for 6-32 screws. People might think right away: "I'll have to tap threaded holes into my case."
You could, but don't need to. Instead, you go to the local metal shop, get two 1/4"x2"x12" pieces of aluminum or steel. Aluminum works easier -- obviously. Cut to the width of the case; tap four 6-32 holes for each wheel -- careful measurement and marking are imperative. Then mark two holes on each aluminum bar where the case's rubber feet (6-32 screws) are secured to the case-bottom. You don't thread these holes, just make them wide enough to fit longer 6-32 screws. Drop your case's rubber feet into a plastic bag for storage, and the rest is obvious.
Now -- this could provide an option for water cooling and a radiator placement which would otherwise be impossible if the PSU is mounted in the bottom. Your system is now very sturdily lifted three or so inches off the floor by the caster wheels. If the vent in the case-bottom is insufficient, you could then add more vent holes with a drill and bit -- a tedious process, certainly. But once done, you could either mount fans on the case-exterior bottom, or the radiator itself. IF the radiator is on bottom case exterior, then you need holes to run the tubing with some sort of neat grommet that eliminates any chaffing from the case-metal.
At least, I think this is possible for a square Phobya radiator -- having determined that a 200mm fan will fit next to the PSU in the bottom of a HAF midtower. You might be able to fit a 2x120 radiator. The only obstacle is the hard disk cage in the forward case.