I wanted to make use of what seemed to me like wasted space on the back side of my O11D XL.
I live in a new build flat that really traps heat and air temps easily hit 30c+ in summer. 3 internal rads set to intake were just too noisy when trying to keep the water below 36.
I bought 3x480mm Bykski 30mm RC radiators and strapped them to the side by drilling holes in the back of the case and installing some low quality knock offs of the Noctua desk fan bracket, from Amazon. I've used a secondhand EK pump res combo to add flow (already one inside the case), but may change that to an external dual pump setup in the near future (keeping the res inside the case).
The back of the case and routing to external rad is a bit rough but I've ordered an i/o bracket along with an Ampinel and will tidy that up in future.
Why not just get a mo-ra? Because this was cheaper and lighter, and arguably performs a touch better from what I'd read. I wanted to hang it from the side of the case to maximise desk space. No issues with balance as the case and kit inside it is so damned heavy.
Performs great. Stabilised at roughly 5c above ambient while playing Doom and Avatar recently, both pushing the 5090 to just 500-550W, with fans basically inaudible at 1,100rpm (window open to the city so not perfectly silent room). CPU is a 7800X3D. Without the external rads, the T30s inside were at 2,500rpm trying to keep the water at 36c.
Just thought I'd share. Not beautiful, but noise problem solved 😁