In general, the de-rig is just the reverse of the rig, but here are some extra pointers:
When bringing the fuselage onto the belly dolly, make sure you remove the tail dolly. The fuse' should be dragged onto the belly dolly so that the leading edge of the dolly is in line with the 'B' on the ASW 19B
B lettering on the side of the fuse. This means it will seat nicely in the trailer. This can be tricky. If it's being really stubborn, pull the fuse on further once the wings are removed. When packing up, avoid putting the tow out gear in the front (tow hook end) of the trailer as it can easily be squashed when the lid comes down.
Make sure to lock the trailer when you leave. The back door is tricky. Lean on the RHS of the lid and you should be able to close the door.