To prevent condensation you would have to have a sealed case. Closed air inside of the case. Pretty much a custom job.
Ive seen someone do the closed case for a different reason, to prevent all condensation for his TEC and water chilled parts.
What you could do is custom build a case that was airtight for all your pc components. Run dongles for your connectors to the outside. Then what you could do is rip apart an old air conditioner or fridge or DIY some sort of phase change system. Wouldnt have to be large. The evaporator would preferably be a finned unit similar to a condensor. You would run your evap with a fan inside of the case, then have the condensor, compressor and all other parts outside of the case: removing heat from case to outside air.
So... Emphasis on AIR TIGHT = No condensation = refridgerated case air.