First of all it NEEDS brakes by law if it has the capacity to have a cossie on it. Max unbraked is 750kg gross.

Secondly, the towing limit of a cavalier will likely be around 1300kg. If the maximum autorised mass of the trailer and cossie is less than this fine, but I doubt it.

Finally, if you're on a pst '97 license, then you will struggle to get around the rules, as starting with a 1300kg cossie, even if you found a trailer with an 1800MAM, you would then be over your license limit with the towcar and trailer.

IMHO the biggest common combination you can do is something like a 900kg car on a 400kg trailer with an MAM of 1300kg, behind a mondeo which is a little over 1300kg unladen, and around 2 tonnes MAM, giving a combined MAM of 3300kg.