A little pricey, but it’s a brilliant idea. - Magpul Industries DAKA Grid Organizer for Pelican Vault

These sturdy styrofoam blocks make it possible to switch rifles and accessories in the same Pelican Vault case. As you might imagine, custom cutting a foam insert provides a better fit than this product, but the flexibility makes it a winner. I can put two rifles in my case, or only one rifle with all it’s accessories and some ammo boxes. There are enough blocks to do almost anything I want.