Thread resurrection time since those covers get sun dried and broken:
Home Depot in your choice of colors for $6.38:
Press off the base.
Use a fly cutter to make the big hole.
Use a drill and then multitool to cut the bottom of the pot itself.
Use the fly cutter to make the big hole in the base piece.
At 2.5" from the bottom (same height as the black original) use a spade bit to drill 1" holes every 1.8".
Press the base back on. I simply put some butyl tape around the solar cell to stick the new cover in place.
The gray is pretty close to the original hull color.
Next will be replacing the fan with a 12V computer fan, but there's a big to-do list before that gets done. The computer fans are cheap and draw very little power, plus the batteries on the boat are continuously charged by solar.