All the foams I've seen at fabric stores have been open cell foam which can rust firearms pretty quickly. I've got a Pelican 1750 which might fit all three. Both of my rifles are fairly small. It's a henry frontier .22lr 24" and a remington 700 .243 short action with a 22" barrel and a scope. The shotgun is a 20 or 22", can't remember just this minute, mossberg 535. Random selection I know but it's what I have. Lever action ftw btw.
The other case is a storm case of the same length but 4" deep and about 6 to 7 inches wide. I think I can fit all three if I set them side by side like some of the high capacity pistol cases with 8 handguns.
I've checked out some of the, design your own foam, places but their prices are astronomical 90% of the time and their layout tools are soso. I don't mind paying good money for quality work but I have a foam cutter here and plenty of other tools to cut and finish my own foam. I figured I could buy a big sheet to play with and save some money on the side by getting the unwprked material.
I've been doing more research and I think It's just going to cost me a hundred bucks to get quality foam that won't damage the firearm. I have a first batch henry and it's my baby but I'm too cheap to buy a full sized safe for my five gun collection right now. I got the cases for free and they have two large desiccant kits each right now so they can keep my guns out of the salty seaside breeze where I live. My hammers here rust overnight.