The Caravan Club and Camping and Caravan Club have some excellent on line guides about all aspects of caravanning. The definition of payload changed a few years back so be sure you understand the nuances. It now makes modern vans look as if they have lower payloads when in fact they can be comparable to the previous definitions when you understand what is and what isn't included. Basically about ten years ago your van Mass. In Running Order didn't include much other than the van ex works. No gas bottles, no liquid allowance, no battery etc and that still how vans come. But now some thing are included for weight purposes even though you have to provide them! Once those things are in the van the rest is basically payload. Quaint ways us caravanners. Also make sure your licence covers you for outfits above 3500 kg and the Club guides explains this restriction. It's based on the makers fully loaded weight of car and van so something like a Mondeo estate towing a 1500kg MTPLM van will likely exceed the 3500kg limit even though neither the car nor van are loaded. Its what they could be loaded to not what they are loaded too.