I successfully made a custom 48' Therm-a-rest Neoair It started it's life a a regular neoair I found at a REI garage sale for $27.73.
Tag said used a few times won't hold air can't find leak. It had two holes in it about 48' from the top a big two inch verticle gash and a smaller hole next to it. I watched a youtube video http://www.suluk46.com/RandD%20-%20RD6%20Neoair%20Modification.html showing how to cut and reseal a neoair to cut weight. I cut it below the slash and resealed it. It was easy 5 minuets and it actualy sealed. Tools required home iron, scissors, ironing board. I now have a great pad for my girls to take out next weekend.