I've been giving foam case inserts a lot of thought lately, and may have a suggestion (which I have not yet, but will soon be trying myself).
My understanding is that the foam being used is usually of the open cell variety. My internet searches seems to also reveal that this type of foam attract and retains moisture, and may be leading to corrosion issues. If I am wrong about this, I'd welcome a heads-up.
Well, I recently attended another Comics (etc.) Fan Fest in Phoenix, and locked onto the foam being used in Cosplay costumes. It
is a closed cell foam being describes as EVA foam. It's the stuff you see being used for comfort floor mats, and most of us have walked on it often without even realizing it.
It tends to be stiffer than open cell foam, also works well for cheek rests, etc., and
is readily available from craft suppliers, Amazon, and the like, but may be most easily obtained form automotive body shops. It may also be less attractive and retentive regarding moisture.
I think it may have value in shooting applications (including as self-healing targets, and target backers), suggest it be investigated for possible applications in our activities.
Greg