@InVOLuntary
This is good advice for sure, and I am sure the other stuff he recommended for sealant is as well. The Zip system is truly airtight and easy to install...just sheeting normally with plywood and then taping the seams with Ziptape. Ziptape is THE best tape on earth. Its stickier than even the most expensive self adhesive flashings and its strong. Its so sticky that if you're new to using it and it gets stuck to your fingertips a few times, they are raw because it's removing layers of skin. Awesome stuff. Regular 4in tape for flat seams is about $25 a roll but they go a long way. I keep a roll of Ziptape in my vehicle and 1 at the house because its good for a lot of things besides its intended purpose. Basically anything you would think about duct taping can be done much better with Ziptape. You can buy the tape at Lowes, but I don't know if they stock the sheets? Lumber yards will have them if not. Site photos from my 1st apartment complex almost 15 years ago were actually featured on their website, which is pretty cool.
On a side note, that T1-11 bead board is really good stuff. A guy that I go to church with builds really nice storage sheds for a living, and he uses that stuff on them. I have seen them sit unpainted for a few years and that board not warp, rot, etc. With a good coat of paint on it and upkeep I bet it would last forever. I think there are some imposters that make product that looks just like the T1-11...there used to be anyway...but it wasn't made the same and would rot. The real stuff is really good though for sheds, barns etc if installed properly. Anyway, good luck bud. Sounds like you are on the right track.