IIIII don't know if gorilla glue is a great idea with that one. It puffs up a LOT when it dries, and it dries very, very hard making it difficult to sand down. It very well could melt the styrofoam, too. If you need to stick balls together, hot glue and a small wooden rod will work.
I don't know what you need to do exactly, but what I did for my pokeball was cover the styrofoam ball in a thin but even layer of Paperclay, sanded it smooth, spritzed it with sealant, and then painted it with no problem whatsoever.
My method is described in the Pokeball tutorial above.