You can also use the gorilla glue for filling up missing chunks in a foam plane. just put a small amount in a mixing cup, along with a drop of water, mix it up and wait a minute. When it starts to foam up, put a small amount into the void you want to fill, and try to orient it so its either straight up or down. (that way the forming foam blob doesn't pour to one side) When its mostly hard, but not quite dry, it can be easily shaped with an exacto knife.
(Note: I haven't actually done this with gorilla, but with the Elmers poly glue, which is pretty much the same, though doesn't foam as much, I believe)