The long seams were tricky trying to reach inside those tubes. If I remember right, my floor is 84″ long. I’d say think it through before you proceed so you are sure you’ll be able to effectively seal those long seams from the extended tubes. I had some persistent leaks there that I finally sorted out.
Don’t mess with the 3m stuff, I just used it because I couldn’t get Aquaseal in town. Stick with Aquaseal or Seamseal, it cures faster.
My inflatable sleeping pad is 78″ I believe. It’s 1000% better than trying to make one. I’d go that route. $80 for a pad, no time to build, doesn’t leak, works perfect. I also use Exped inflatable camping pillows for seats. They cost $35, don’t leak, fit perfect, and saves time from building the seat kit.
Not doing self bailing, this is a calm water, family boat. If I need self bailing, I’m in water I shouldn’t be in.
Overall this thing is working great. I’ve had it down easy class III alone, and use it several times per week on my boat to get to shore when we anchor our 24′ boat. Will be fishing from it for a few weeks on the Kenai and Kasilof rivers soon.