Vally P asks what the top box is for. A very good question. The answer is, anything you like really, but bulky items which need to be stored on board which you have little space for inside the boat. We have used ours for bags of coal and logs, brushes and mops, TV ariel, bits of fishing tackle etc. Vally has a big boat, so probably has no use for one.
Kath fancies getting one or two folding bikes, which could be kept there if they would fit. If that happened we'd have to chain them for security to a U bolt inside the box. Then the immense thickness of the box sides would come in handy.