Shiplap siding is very simple to install, all you need to do is start the process correctly! If there is any discrepancy you are doomed from the start, so take your time to make sure it is perfect!
The first thing you need to do is install the starter strip. A starter strip is merely a ripped section of fiber cement board that is set at the bottom of the first plank. It should be around 2 inches wide and run the length of the wall discontinuously. If the starter strip is continuous, water running down the wall between the siding and wrapping will become trapped between the siding and starter strip. By installing segmented pieces, water is able to drain out through the gaps at the bottom of the wall.
I installed two strips with a nice gap between them and a nice gap near the corners. With these two strips in place, the first plank can be installed.
The first plank is the most important to get straight. On a trailer, there is little that is level. The trailer is probably not on level ground, so a bubble level is pretty much useless. Instead, a fixed known reference point must be used. In our case, the trailer is known to be perfectly flat.
Since the trailer is flat, I can feel safe about using its front edge as a reference point to level the first plank. I set the first plank to overhang the top lip of the trailer by 1/2 of an inch. I propped the plank against the tiny house wall and measured the overhang on the trailer by the prescribed distance. I then verified that it was the same on the other side. Once everything was 1/2 inch of overhang, I screwed it into the tiny house.
With the first plank attached, I then proceeded to set and attach the planks one after another all the way up the front of the house.
With the first plank set properly, all the other planks went on smoothly and easily. As you can see, the planks all went on straight and even, using the simple tool I fabricated out of a metal strap.