Hi Tugster, It's not as complicated as it seems,yes the 1008 quoted in your book is the size of awning you require, that size is the measurement from the ground at the front of your van up and along the awning rail to the ground at the rear whilst the van is level and on level ground.Most awning manufactures give a size that will accomodate a number of different vans eg 925 - 950, as long as the awning you buy comes within these measurements you should have no problem. If you buy a porch awning then you need to take into account where on your van the awning is going to sit, obviously you want it to cover the door but depending on the measurement you need to check if it is going to cover half the window for instance. Hope this makes things a little clearer for you, but if you are buying from a dealer whether its new or second hand make sure they Know what van you have and most will advise you accordingly.Make sure you are 100% happy before parting with any money as the wrong awning can be a very expensive mistake.