Cliff, Can you mount a regular case fan below the GPU? If so, mount one there blowing directly up into the GPU. Make sure you have a filter below the fan though. If the case doesn't have one, you can buy a magnetic filter real cheap.
I could mount up to 3 x 120mm fans on the base., I was thinkin of maybe two, for increased air flow.
Steve the reason is, when I'm benchmarking with Performance Test, I get lower disk scores, because my Samsung 512Gb PM 951 M.2 NVMe SSD sits between my CPU & GPU(NOT a good place for an M.2 slot MSI) and the SSD starts to thermal throttle, so I need to get the heat away from it quicker.
The Samsung PCIe SSds Have a reputation for doing that.
Nice water cooling in your case.