I would first do some measuring. Establish the height of the foam and shape of the back,top,sides and the part that keeps the buns cozy. I would use a cardboard template for that. Measure from the furthest point to the furthest point with your template sayyyyy duct taped in place to keep it standing or whatever while you measure following that shape tightly. Measure it and add a foot for good luck so you can rough fit the material over the foam etc, and work with it. The shape of the templates will be the shape of the foam you will carve out evenly and consistantly to that height, width etc. Hope that helps, the foam part is easy,...you,ll need machones to sew that to slip over the cushioning.