Thanks for the replies so quickly! The trailer has 3 steps..open. He has never used a ramp before, so I like the idea from Old-Biscuit about laying the ramp flat and having him walk on it that way.
My husband has a truck and Cruiser will jump up in it just fine. I just think he is scared of this trailer and maybe not knowing what is in there.
He had been picked up as a stray and so I don't know his history, but he has been "leery" of men since we got him. He will ride on the front seat with my husband in the truck, but any other time, he just shies away. I suspect he may have been mistreated in the past.
Our Vet is the one who suggested the ramp...she also suggested putting his food in the trailer and see if that works.