I say 'trying' because I'm making it up as I go along so it could turn into something completely different!!!
I bought an off cut of patterned canvas, some strapping and water proof lining.
See, all this is in my head with a lovely strong shopping bag at the end of my endeavours. However, when I started to write the instructions down, I could see problems and the construction wouldn't have worked. I've now just decided to go for it and see what happens. I do have my quick unpick at the ready though!!!! LOL.