Printed Version 1  for a one pound round weight, for dome trim it was more weight than needed. V2 was printed to accommodate 3/4 inch rod. I use stainless for the weight about 62mm long. Both are designed to move weight forward or back to optimize balance point. The funck in the leading edge in V2 is some left over support. I will be happy to share STL files if there is any interest.

Just a follow up on his project. Tested and it worked as expected. Except the double tape attaching the weight to the dome shade came loose in the water. I used 4 3mm machine bolts to attach GoPro holder to dome shade for a positive fix. The tape(Gorilla double sided mounting tape) work well in no weight situations, but not to hold 500 grams.