Try it out. Have fun. You should be able to build a reasonable seat cheaply if you have some foam around. You will also need to put in anchors for thigh straps, especially if you want to roll it. You can just glass in small loops of webbing or cord to hold the straps. Just make sure you can release them if necessary.

You really need to look at a C1 to see how the seat and thigh straps are installed.