John, you want to know how water tight PMF is?


A few years ago I picked up a couple of Priority boxes from my local post office and did an experiment to find out the answer to that question. I painted the inside of the box with TB2 and the lined the inside of the box with a "Jersey" bed sheet. I then used the TB2 on it again to soak the material and let it dry before I primed it and painted it.
Once they dried, I filled them with water and waited. After more than a week, it still hadn't leaked.
John, I'm not disrespecting you or trying to be hurtful when I say this. As a matter of fact, I'm trying to be encouraging to you when I say this. Buddy, you haven't built a camper yet, and you haven't done any experiments yet, however, you are our #1 Doubting Thomas. It's time for you to roll up your sleeves and get to work.
I suggest you pick up a bottle of TB2, take some old bed sheets, get a few cardboard boxes and try this experiment yourself. Do it several different ways. Try it with and without the primer and paint. Try it with just the TB2 and the sheets. Find a way that works. Do this right an you'll turn some cardboard boxes into buckets.
I'm looking forward to a thread of your experiment with a lot of pictures.

Never argue with an idiot. They will bring you down to their level and beat you with experience.