For foam repairs (and I do a lot of them), I mostly use ProBond Polyurathane glue. You can get it at the local hardware store. Gorillia glue is the same stuff.

It's advantage when working with foam is that you put glue on one part, and mist the other with water. put them together and hold with tape. The glue will foam up and fill in any voids and places where the joint isn't quite there. And it's a lot lighter than epoxy for this kind of thing.

The actual technique of cutting out a block and filling it in with scrap is right on. I usually cut a trapazoid instead of a square though. Just makes it easier to work with.

Depending on the damage, you may not need to more than just tape over it though. It depends on the type of foam and the type of construction of the plane, so I really need more information.

On the other hand, when something on my GWS A-10 breaks, I usually use foam safe CA, as it's lighter and makes less of a mess, and is plenty strong for the light weight white foam.