This was my first attempt at building the interior as well, and was very happy with how it turned out.
1. Color as needed
2. Cut out along the outside lines of the trailer (inside lines that need cutting are labeled)
3. If putting in the interior you will need to cut along the lines for the door, as well as cut out the windows so you can see in and install the interior.
3. Glue any of the tabs with a dot to assemble. If a number is on the tab, it is glued to the same number somewhere else on the template.