Do I have to give back my r.v. that my son gave to me as a gift?

you do  not have to (except in unusual circumstances not present here) return an unconditional  gift.  Once it is given, it is yours.  However, your son may have a different story, for example he may claim that he was only lending it to you to allow you to use it for a while, or that you were supposed to give him somehting in exchange, or some other story, and it is always possible that the judge/jury will believe him.  The fact that he kept title in his name would tend to support such a claim.