I bought a trailer from eBay last year for £23 and I've found that quite useful, seems a shame to build on it.
Anyway, I started building about a week or so ago, but at the moment I'm having trouble sourcing some 20mm insulated sheeting for the 'wall sandwich', was supposed to be 25mm but for some reason they sell 25mm planed which is actually 20-22mm!
I'll start a build thread soon

While I'm here, I'm building using plywood, what is the best way to waterproof it (I mean brush on stain/varnish/whatever)?
Thanks, Lee