Motorcycle carrier

Bonneville70

We carry a scooter on our motorhome which puts us right on the rear axle weight limit. We would like to carry one of our motorcycles which of course weigh far more than the scooter. A number of times whilst abroad we have seen fixed trailers on foreign motorhomes
which have a central wheel to take the weight instead of it being on the rear axle. Can anyone give us any information on these please?