[2]Something like this fan. It would be mounted to blow out the back of the case through the mesh I was talking about. Could probably mount one above the gpu and blow out the slot right above the gpu depending on the size of the fan chosen.
No plans to water cool. I just ran across some posts that showed people testing 40mm - 90mm fans below the gpus. They cooled better as exhaust fans than intake fans. Theory being that it was removing the hot air around the gpu pulling fresh cool air from the front intakes toward the gpu. I am sure it varies what works better from case to case and fan setup, but was interesting.
Reason I started thinking about this was my rx570 is undervolted and overclocked and stays around 78 while gaming. The XFX backplate doesn't use thermal pads or anything to draw heat, but it is pretty warm to the touch. Also removing the side panel didn't seem to change the temperature more than 1 degree. So, I was thinking maybe hot air was just seating near the gpu. Or, that is all the factory heatsink can do. I also thought about removing the stock shroud / fans, and putting a pair of 120mm fans on it. Probably cool better and be quieter. I have seen that done with good results.
[1]Could try a pusher 120mm fan at the end of the card to help push the air from the front of the case across the front and back of the card. I haven't seen that done, but it might help some with larger cases where the front fans are farther away from the gpu.