My dumb air saddle

I need someone to help me figure out how to put the tube in the cover and get it to stay. I bought this stuff from

Sew the dogbone air pillow in half to turn it into a single layer air pillow. Find some foam (Miyata foam, Torker LX foam, Torker DX foam, Viscount foam, KH foam, or anything similar like 1" thick carpet foam). Then put the saddle together like this.