Agree with the above - built mine about four years ago, as there was nothing available over here. This is an old pic and has had a few changes over the years. I've seen quite a few based on Sankeys. Also, Adventure Trailers now have an outlet in the uk:
http://www.adventuretrailers.eu/
However, I just don't think we have the open space that they do over the pond. Plus there's very few 'wild camping' opportunities in the UK. That's not to say you shouldn't do it, but having been in the trailer industry for nearly a couple of decades now, I'd say your client base would be quite small and you'd be looking at low volume sales. Don't forget, if you want to sell them, you'll now need to have full EU Type Approval, which is a costly excercise. I know of several manufacturers (generally of boat trailers) that have had to close their businesses due to the cost of getting their trailers type approved - it just wasn't economically viable. Not only that, you'd have to be competetive, as I know from experience that the majority of the UK are pretty tight when it comes to trailers! Happy to spend £40k on a RIB, but find it hard to part with £2k to put a good trailer underneath it!
The above may sound like I'm trying to put you off, but I'm genuinely not. Just saying there's a lot to consider. If you have an idea, believe in your product, have considered everything required and are committed, then go for it
All the best