I think I remember reading somewhere that the floats were coated to prevent any bits falling off and clogging fuel system.I’ve also read that there is a fungus that can attack the cork and cause it to break down and coating prevented that.I have no idea whether either is true.
I’ve not tried, but I understand the floats can be made of balsa wood. I’m sure that these would have to be coated, I would use hot fuel proof dope. Balsa would allow much flexibility in carving the necessary shape.