Dog won't go into RV

I have the same problem with one of my dogs. We used to have a travel trailer that was fairly close to the ground. It only had 2 steps and my dog would jump into the trailer, right over the stairs. Now we have a motor home that has 5 steps. He is petrified of the stairs and I have to carry him up and down the stairs. While I am holding him, he has the "death grip" on me. I don't know why he doesn't like the stairs. We have had him since he was a puppy so I know he has not had a bad experience with stairs in the past. Luckily he is only a little over 20lbs so he isn't too heavy to carry into the motor home. He loves being in the motor home.