I'd book direct with the RAH Bobbi. Package tickets are often way up in the Gods and rarely include train tickets. A coach/hotel/ticket package might be a more likely find.
I have just looked at the RAH site and the current Proms must have created a rush on tickets. I clicked on the November concert and was number 78 in the queue, so don't delay whatever you decide to do.
watched it and was disappointed at the choice of musicals
I never liked Carousel or Oklahoma or Guys and Dolls.
There are so many brilliant musicals out there - the music would have been wonderful and sorry enjoyed the black guy singing Clarke ? - rest were just mediocre.