Those taking up residency, holiday home owners or with business in Spain can import their vehicle into Spain and are only exempt from import duty if taking up residency. It will be considered that you are importing vehicle as your personal goods. You must have been the legal owner of the vehicle for at least six months before applying to put the vehicle onto Spanish plates. Import documentation should be completed within 60 days of residency status.
Non Spanish plated vehicles can only be in Spain for six months (nonresidents) Residents can only drive a non Spanish plated vehicle if the owner of the vehicle is in the car with them or if they´re still within the window of importing it, see above or if not part of household goods, 30 days.
Nonresidents can also put vehicles onto Spanish plates but will not be exempt from the duty payable. (please check with the DGT or a gestor de automoviles before making the decision to bring in a foreign plated car).
As a general rule, commercial vehicles, vans trucks and motorhomes which are right hand drive, cannot be put onto Spanish plates. Saying this, do talk with a good gestoria de automoviles as there may be exceptions depending on type. In general if motorhomes are factory built and registered new as a camper then RHD or LHD should make no difference. Anything that was converted outside of Spain is not possible to re-matriculate. There are workshops that can certify conversions but not on a RHD commercial, only on LHD.
Though providing general information from EU site, please consider that some EU countries have their own regulations.
It is advisable that you instruct a good ‘Gestoria de Automoviles’ to carry out the registration for you.