I had to think through this one a bit. I’m not a 3D designer by any stretch of the imagination. Instead of using a nifty 3D application to model this I used pencil, paper, and Adobe Illustrator to lay things out.
Cardboard was the testing ground. Looks good. Should be very very strong made from marine plywood.
Tsunamiball 
Chris, I have taken it on to educate the general public regarding the proper name of the paper product you have used to create your mock-up of your capsule. It is called “corrugated paper” and kraft paper is generally used in varying weights and thicknesses depending on its uses. Cardboard is generally a single-ply product without a fluted core.
Michelle,
Noted. Thanks.
-Chris