The top and bottom trundle support (#7 and #8 in manual) wooden planks are about an inch shorter than the width (pics attached), which looks like a design flaw. I am worried this will make the structure weaker, since the slats and the mattress would be on top.
Further, its better to use a drill (and not a screw driver as mentioned in the installation manual) for all the wood screws, while installing the drawers and slats.