Trans dogs in cars through spain

We have finally got a dog ferry boat on oct to come to mollina area. I understand our dogs need to have sest belts on and muzzels on when out in public. But we have had conflicting stories abt the dogs been on boxes/cages. We have a huge giant lab that stands shoulders & head higher than normal labs ( he came from a line of over 10 ,linerage of working dogs for shooting birds and grouse etc working dogs) ours is a big softie and there is no way he would go in a cage/crate in the car as it is he takes up the full size back seat and he would have to share with our medium legged JR. Plz can anyone confirm and do we have to have all the dogs papers trans in spanish to???? Many thanks carol xxxxc Sally our JR is smaller that Charlie's "bum" lol hence our prob cxx