When to run this? Two suggested things to consider:
1. A lot depends on your potential or expected audiance and where they are willing to travel from for just one charter. With the cost of charters going up, perhaps a scheule that allows those from out of state to particpate in other charters is an option. The SLRG often runs a 3-4 day steam charter in late September. Also the D&S usually runs a two day fall charter in September. Why not try to schedule around these days, giving folks a day off to travel between railroads. This might bring in more that need to travel and justify expenses.
Likewise, if you want winter "steam shots" the D&S usually has a winter photo special. This could be an attraction as well. Yes, there is no guarantee of snow, but steam/smoke shots in the cold can be really great.
2. Look at running 2 out of 3 or 3 out of 4 days. Give folks a window, and the railroad, to schedule around weather issues. This is being done by at least one Swiss group for a Sept 2014 (early Sept) trip with charter steam. They will run for 3 of the 4 days Mon-Fri (when the railroad is not running tourist trains) and will make on the spot decisions as to which days they run. Down side is you have to book hotels and travel for the full 4 days, up side is you get a better chance of getting the weather you want.
All of these require some compromise, but with todays charter costs everone needs to look at options.
2.