What additional step is required when cutting traupalins for sections?

When cutting traupalins for sections, it's essential to account for the added material needed for proper fitting and securing the sections together. Cutting 15mm extra from each side allows for this margin, ensuring that the traupalins overlap or fit snugly without leaving gaps. This extra allowance helps accommodate any discrepancies that might arise during installation and provides a better seal, which is crucial for maintaining the integrity of the dry van.

The other options, while they may seem helpful in their own contexts, do not specifically address the requirements for cutting traupalins effectively. Measuring twice is generally good practice, but it does not provide for the specific additional material needed. The use of a power saw could help in cutting through the material, but it doesn’t pertain to the margin requirement. Marking edges with a pen could assist in precision but again doesn't fulfill the specific need for the extra material that ensures a proper fit. Therefore, the best practice when cutting traupalins is to add that 15mm on each side to allow for effective installation.