In any case I wouldn't expect an insurer to pay out if there was an accident and your trailer was overloaded, not roadworthy or, for example, not fitted with a secondary connection device. Equally, if the driver's license didn't cover it.
I once rang my insurer to tell them I had just fitted a towbar to my car. They weren't bothered in any way - despite the fact I had effectively just added a very solid 'spike' to the rear of my car.
"Can ye model it? For if ye can, ye understand it, and if ye canna, ye dinna!" - Lord kelvin