For making right angles a T-square is indispensable, preferable a large size, at least half a meter or more, as a mistake is easily made. Make sure that the floor of the van is water level. The van is not always perfect in this respect, that is a perfect even floor, and the wall is usually slooping towards the top and therefore the ceiling is 10-20 cm or even more less wide than the floor. It depends whether you want to make a rectangular wall or want to use the space which is otherwise lost. In the bedroom part I used flexible 5,5mm wall mounted to the ribs to have a bed length of 185cm, but the wall in the seating area was a 12 mm wall, almost straight, because I used it to make a window frame and to mount sockets and control panels for water and heater. Moreover this was a good connection to mount the water tank and make a bench and also a good connection with the elevated floor which was necessary for a good transition to the driver’s section. Underneath this elevated floor there was room for water hoses, pump, expansion vessel, heater and electricity wires. I did not figure it out exactly, but in some way it worked out well, which was more luck than logical sense. Of course I made several mistakes, but they also could be corrected by using wood clamps and wood glue. If the edge of a plate had to be corrected, this was the ideal way. Apart from that clamps are also indispensable when sawing with a jig saw (see below).