Here is the very ugly and very comfortable pad I have made. Hillbilly engineered from white closed cell foam, then covered with a thin layer of the black foam. To make the 'dished' area I used the wedged shaped foam that is used to form the wall berm at the bottom of above ground swimming pools. Readily available at pool stores. Used 3m super 77 to glue it all together. It all held in place with small diameter bungee cord. I can move it forward and back, to give me different seating positions as I go. I will cover it with high quality vinyl soon. The seat beads keep the boys cool!