This costume is right up my alley!
I love seeing people use foam fabrication. It is a method I really admire.
You are using it masterfully.
If you spray the costume with spray glue on the outside before you add the latex it will seal the foam so the latex doesn't soak in. That way the latex
will sit on the surface. This not only saves you latex, but makes the costume lighter.
There are spray glues that are colored. Those help you see were you have sprayed.
Another way to save on latex is to add paint to the base layers, This helps you see where you have placed latex and gets the base color down.