A little late now, but I bought an aluminum, rugged case, from Amazon. It was already shaped for the Phantom and a LOT of accessories for a hundred. I think it was a great deal and it looks very professional.
I have heard of electric knives being used. But, if it is a solid block of foam, it is very hard to cut the bottom of a hole flat. Unless, you cut the foam in slices. I read a post where a guy used a wire, heated by current. He did the multiple,slice method to get smooth bottoms. I think the pluck able foam works better than a solid block.
There are companies that will cut the foam to fit your box and parts, but the price is rather steep.