I looks as though you will have to test the waters with different dealers or independent workshops as who would be willing to carry out any warranty work if needed, if you give them the servicing work. As Marquis as the original supplier there contract is with the first owner. And as they are not transferring the ownership to you looks as though they are not prepared to take on any work as they are not obliged to do. I think you will probably have fingers crossed and hope there is nothing requiring attention evolves. My friend was in a similar position when he privately bought a 4 month old caravan from a seller who after one weeks use,decided it was not for them. Fortunately the problem he had was not major and only cost him under £1000.