Trophy towbar

My Trophy, born 1992,   has a long rear overhang  where the bathroom is.

I would love to fit a towbar to enable me to carry my husband's power chair in a small box trailer attached to the rear of the van. .....  Having to carry the wheelchair in the van is a real inconvenience and  when parked, of course, the chair has to sit outside.  Not v safe. 

I live in Hampshire and have met lots of fitters who have scratched their heads, tut-tutted, and sent me away..  Apparently it CAN be done but not by them.....!

 Any info or advice? 

We are willing to travel if necessary - it's a good time to get this kind of work done during the winter.