Exterior Boot Box/Rack for Fourtrak

Forum: 

So I saw this and it gave me an idea:

http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_172555_langId_-1_categoryId_165477

I need extra space to carry three LARGE kit bags, and my fourtrak has the towbar kit. If I remove the tow hook there is a very sturdy piece of steel with four bolt holes. I was thinking it would be possible to manufacture a sort of rear tray out of steel that bolts onto these four holes and rests on top of the rear bumper, sticking out about 2 feet. I could also extend it up so that it bolts onto the spare tyre mount for extra sturdiness. It could then be finished off with a light board for extra lights and numberplate. It could also be designed to allow quick release so it'd be possible to open the back door without having to undo four bolts.

As far as I can see this would be a totally solid device (much more sturdy than that Thule thing which I think clips on to the boot closure). Also it would be preferable to a roof rack which overloads the sills causing cracks and leaks (already happened on mine due to previous owners, fixed with silicone sealant).

Has anyone tried anything similar?
Does anyone know any legal issues associated with such a device?

Boxing Clever

Basically they are illegal, so would not advise manufacturing and fitting one, unfortunately they will attract the attention of the Police, and they will have a field day.