Try Towsure,they have a good range of trailers and also you can add to them too,as we had one and the price's are well good to,much cheaper than Motorworld,well the cheapest we have ever come across.
We,have just bought the Caddy 535,larger than the 530,but not ridiculously sized. We paid £339 for it and £29 for a spare wheel. Really great trailer,we have a huge tent and loads of "stuff" and it is plenty big enough.
We purchased a DUUO too. Folds up and stores on end takes up half the room of any other trailer on end because the wheels store inside the box and don't stick out. It can be wheeled around even on its end. Tows absolutely superb, no bouncing around all over the road when only part loaded either unlike some cheaper trailers.
Whichever trailer you decide to get BARTER!!! I got the spare wheel, cover and a hitch lock thrown in - you don't ask you don't get!!!!
Nearly forgot - the Duuo is a bit deeper than similar trailers which is superb for all your camping equipment. Would highly reccommend one.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.