Hello, Stephen, it is still amazing that I am able to post info to folks that are on the other side of the pond. I assume you are planning on building a traditional teardrop trailer, which must include: a bed for two, a galley in the rear, under a hatch lid, and be low enough, so you can not stand up within it. I am afraid I don't know what you mean, about building a travel van, unless it is a bit bigger than a teardrop trailer, (probably a stand-up caravan). I am sure you are aware that the typical airsteam camping trailer, is nothing like our little teardrop units, and if you are really planning on a true teardrop trailer, be aware that there are many styles and shapes that you have must decide upon.
There are a bunch of folks over there on the other side of the pond, that are in the process, or are contemplating building one, and it would be helpful for you, to contact them and get a few pointers from their experience, prior to your actual construction. I understand that the UK trailer rules are not as lax as those that we have here in the US. Info is available here on the teardrop forum, that could give you a heads-up about the ins and outs of building and licensing one of our wonderful little camping units. Check it out, ask questions as you go along, and by all means, take pics and post them, as we love pics. When completed, be sure to load it onto an ocean cargo steamer and upon landing on our shores, plan on a cross country trip across the USA. Now, when you get to the west coast, swing on by and see me, the coffe (or perhaps, tea) is always on and we can chat and tell teardrop lies, which many of us tell, since we broke away from the Queen's rule, so many years ago. There is plenty of room in my driveway, for UK builders and travelers.

Roly, the li'l ol' So Calif woody guy.