I have to sound a note of caution about tow matching websites, It has been established that their data bases are incomplete, and that some of the data they hold is actually wrong.
If you intend to use one, make absolutely sure that the make, model, trim level, engine power, body shape and year are exactly right. Do not assume that similar models have the same characteristics; there are some notable instances where the same product from the same factory but with a different name (eg, Vauxhall /Opel) has different limits applied.
It’s not difficult to check your self, just make sure the details you have in your vehicle and caravan documentation and identification plates match exactly what the web site says.