andyman said:Don't you slot them into the slots on the bottom tray, although I did notice not the strongest of hold doing that
The slots on mine aren't great. About 100mm from the back of the slot there is a piece on plastic that crosses the slot. This piece prevents the rails from going deeper into the slot. Slots work ok on a smooth surface. I don't trust it up/down stairs. Also I don't want to tighten the strap too tight for fear of bending a rail.