As promised, I'll do a little review of the finished product.
To date, I have made 4 pads. Costs tend to run about 65-70 dollars per pad with two valves, 18 oz pvc tarp, foam, and glue. I was a little worried about using glue for the pads after all the negative talk glued PVC boats get, but I've been happy with the results. The original prototype has around 15 sleeping days on it and 15 uses as a pad on the raft during the day. With all the folding, smashing, walking, smashing, and splashing that goes on. The other 3 were made and used on our recent Deso trip of 4 days and nights.
In general, I'm very pleased with the result. My parents went on this recent trip and my dad hasn't slept in a tent in at least 12 years. The pads made the trip much nicer. They slept well, it softened sitting on the raft, and provided some added insulation to a cooler on it's last leg. We liked the foam. The PVC material was durable and I really liked the white color. Heat was never an issue, sometimes darker color pads really get hot.
The seams held up well, even after repeated rolling and smashing. Getting the ends to seal evenly and securely without folds was definitely the hardest part of the process. Doing that correctly and getting the material to fold over and create a tight seam was particularly time consuming. While I'm on break from school and have a lot more time than I have money, the investment made sense, but I'm sure there will be a lot of folks out there who would say the time/frustration of sealing things well would not be worth it.
As I've said in the thread above, the real value in pads is durability. 15 days is a nice start and I'm happy with my investment, but it will be interesting to see how they stand up to years of abuse. It was fun to try it out and prove that it can be done. I'm sure the material is top quality and will not be a problem. I think the glue will be durable and resilient. It is used to fix tears in PVC tarps that protect loads on semi trucks traveling and flapping at highway speeds.
Thanks for the support and input.