Have a look on the wheels, there should be a date code which will give you a rough idea.
What colour is the canvas? The canvas changes from green to blue around 2007/8.
There used to be a Trigano owners group on Yahoo where we had a spreadsheet of serial numbers but the folding campers were not included. The only way I'm aware of dating is by the datestamp on the wheels.
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.