Hey Derek,
Great build. I’m actually just starting on building my own plus-size voyageur, but even larger to accommodate two kids (about 100″ long).
Any other general tips you want to share? It sounds like sealing that inside tube seam during construction might be a good approach. I have loads of Aquaseal but none of the 3M stuff you referenced.
I bought fabric to make an inflatable floor, but your backpacking airpad idea would be a nice time saver. Are you planning on gluing attachment points or anything to the pad, and then fastening from there to attachment points on the raft?
Also, are you making it self-bailing? I decided to and Matt recommended closable drain-valves which I thought was a great idea. So on the mellowest water we can just keep them closed.
Thanks.