Mobile mechanics and warranty

Can anyone help?  I've bought a motor mover from our local caravan dealer, in the deal they gave me the number for Autowfix who are sending an engineer tomorrow to connect the mover.  I've asked both the Autofix contact and the engineer if they are registered to then National Caravan Council, both didn't answer!  The engineer just said 'well i work for a company'!  Will my warranty be void if I let them fit the mover?  Can anyone help!!