One of the things you’ll quickly learn about wood when you build a tiny house is that it will never be perfectly straight. You can do your best to select the straightest pieces, but all wood is going to have some warp to it. The trick is that when you build a tiny house, the fact that the space is so small, the tolerances is much smaller than a traditional house. Dealing with warped wood is just part of the game. What is worse is that you can build something very square, but over time it settles, expands, contracts, shifts etc. It can be a tricky thing.
The biggest skill I’ve learned to combat this is the creative use of clamps. Early on in your build you’ll learn a truth: you can never have enough clamps! So here are some photos of the clampings that I’ve had to do during my build so far. I have had quite a few crazier ones, but forgot to take photos.