bought a box trailer last year im thinking of putting a wfp system on it and I will stay on the van and let the lads take the trailer hooked up to his car, his car is insured as normal but I was wondering if he would need to have extra cover for the trailer , not worried about damage to it but just the legal side , so in short do I need extra insurance to tow a trailer the trailer is a 8 by 4 thanx