Do you have some specific organization in mind? The NMRA and NRHS each have a major convention in July, and each have been doing this for years.
I'm going to attend the NRHS convention based in New Philadelphia, Ohio, with the cooperation of the Ohio Central, which is a first class outfit.
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I will ride all the train trips, although not in the most expensive accommodations, and will participate in one of the shop tours, which I know will be worthwhile because I've been there before.
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This will be the first NRHS that I've attended. I've ridden on previous convention trips that were close by (South Jersey), including 1976 (before I joined NRHS)
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NRHS conventions are organized by a local chapter or several local chapters with assistance from the National, and each convention organization does what it can with what's available. A local chapter that's not near any steam operation won't try to outdo Buckeye Rails 2006; they'll do what they can.
Maybe next year's Chattanooga ChooChoo convention will try to outdo this year's convention.