I had originally thought vinyl but contractors trash bags are 3mil thick and very strong and easily sealed with a heat strip. The styrofoam peanuts I mentioned was just a thought. I didn't know they made them out of corn starch. But I have two bags full of real styrofoam I have saved from packing of things I received like the bandsaw I ordered and electronics etc. They are very light and don't absorb water and cost nothing and I can always pull them out if necessary. Once sealed and in place their is very little chance of them leaking. I am 70 years old and paddle on a very shallow river. In the summer when I do most of my paddling it is anywhere to 6" to 10' deep. I have done wet exits and I can easily swim to a shallow spot in a few seconds. I am looking to go cheap. I am not sure I will like either of the SOF boats I have built. One is a 14' freebee from Kudzu plans. The other is a scaled down version of a Greenland that is15' I built from an Instructable instructions. I have two Hurricane Aqua thermoformed Kayaks I bought used one is a Santee 135 which weighs 43lbs after I replaced the original seat with a foam tractor style seat which Kudzu recommends and a back band. The other is a 16.5' Tracer which weighs 45 lbs after replacing it's seat. I love both boats but was fascinated by the SOF kayaks I saw on line but they are turning out to be way more expensive and time consuming to build than I had originally thought. Now I just want to finish skinning them an try them as cheaply as I can. I am not an elitist. My plastic boats are light, cheap, fast, and easy to care for and durable. I am not a craftsman I just want to paddle. I understand your love for the building process and trying to perfect the art. I wish I had started at an younger age. Think cheap! Again thanks for the input.