Watercooling Custom loop water-cooling 400r

Hi all, Im new to the bit-tech forums, so I could use some of your advice and experience.

I recently built a pc in a corsair carbide 400r case and am looking to water-cool it soon, as i did not have the money at the time. I have looked at the corsair h100 cooler as i know that it fits in the top rad mount, but i would like to try a custom kit such as the ones by XSPC. I have looked at the places to mount a rad in the case and am wondering if it is possible to mount a rad to the back of the HDD cage, as there is more room there than in the top of the case as my GPU inst particularly long (sapphire radeon HD 6850).

Do you have any advice or recommendations? Thank you in advance.