JNBrown, don't let CF read your post, I think they laugh at older!
We used to put tandem on trainer but I also think separate training is better. I put my single on the trainer and wife rides a spin bike.
We don't stay "in shape", but it sure is better than totally stopping for the winter. You are correct, "I think the best way to stay in shape for is cycling is, you probably guessed it, cycling."
R&J