EVGA Backplate
  This  backplate cover is made from 2 layers of 3mm acrylic, they will not interfere with your waterblock or any other component unless you are using a micro motherboard, then you would need to measure the distance from the GPU to the ram slots and the audio ports on the rear of the motherboards I/O panel, it is common that there is issues if tthis is the siutuation so check you motherboard for clearance,  these plates are 6mm thick.   I can make them for any GPU so just send me a message at checkout about your model graphics card.