Prof and Birdman , I appreciate your insights . I have never come across these devices , but reading about your experiences and the pitfalls of the hitchdrives means if asked I can advise against them. The other thing that springs to mind is a conventional motor mover locks the road wheels , which if manually reversing a caravan down a slope using one of these hitch drivers , even a handbrake wouldn't stop the caravan if the hitch wheels lost traction , something which people don't realise until it happens.