My family also met them once by accident on a holiday cruise in the Caribbean. They apparently take their family on a vacation every year and just happened to book the same cruise as us.
They were very friendly and down to earth. My father spoke to Jimmy at a book signing event on the ship and asked if he could say a few words to Rosalynn if she was around. Jimmy just said something like "sure, head on in to the back room", which was guarded by a member of secret service who let my dad right in.
Side note: The most fun aspect for teen-aged me was seeing the Carters on a bike ride with two Secret Service agents following in tropical shirts and shorts.