Today, I was working on a smashed-up floater (won’t tell you who the owner is), and used an excellent method to fill gaps.
Super glue is very thin and needs to have the parts perfectly fit together. In other words, it doesn’t bridge gaps well as epoxy or PVA (woodworking) glue does.
However, if you sprinkle some baking soda (bicarbonate of soda) into the gap/hole and then add a few drops of super glue, the result will be an instant and very hard bond. It can be easily sanded.
If it is a deep hole or gap, you may need to work in layers.
On the matter of glues for EPO foam, Multiplex, a major manufacturer of EPO models, doesn’t recommend any other glue than CA (super glue). Epoxy works in certain circumstances, particularly if the glue has something to hold onto, such as rough surfaces of “complicated” fractures after a crash.