Hi John
I have one that i used to fit onto the back of a T4 camper with a fiamma cycle rack. They are quite easy to fit, and have t-head nuts inside the box which you tighten onto shaped metal plates, to pull on u-bolts that fit round the rack. There are 4 fixing points, in a square, top and bottom which align with the main vertical bar of the bike rack. So you have to tighten 8 t-headed nuts, which is easy by hand.
I'm going to use if for my current van as soon as i can get around to it, it used to carry all the kids summers gubbins, or it could take a proper inflateable boat and outboard motor.
The box is dry, and handy, though does attract a bit of traffic muck in the right conditions.
I can't remember what model mine is, its the biggest one though, and i can carry carry it ok, its just a bit of a game storing it.
I would say its a 5 - 10 minute job to put it on or take it off. I keep all the mounting bits in a margarine tub which lives inside the box when its not on the van.
picked mine up at the Stratford show as shop soiled and scratched in 1999, it was 170 quid instead of £250 i think.
Dave