Just add to this idea rather than have Monthly Trips, why have 4 Major Trips Per Year and then if there is further interest, then schedule a few minor Day Trips in Between. As there are Various elements that you have to take into account also for example.

Cost - Can everyone Afford to do these trips on a Monthly Basis - (I know I can't)

Work - People who are in paid Employment - Will they be able to get the time off work to go on a Day Trip.

Trips - Would have been in Reason and Doable in a Day

Here little Model I have came up with, Trips would occur Every 3 Months, for example

February - Day Trip to Carlisle
May - Day Trip to Berwick and the Scottish Borders
August - Day Trip to Edinburgh and Dunfermline (SVBM)
November - Day Trip to Preston (Tour of John Fishwick and Sons Depot) if Possible

Then for Minor Trips in Between we could go to:

Lothian Open Doors Event
Weardale Open Day
Bus and Coach Show (Birmingham NEC Arena)
Showbus (Duxford near Cambridge in September)
Exeter Bus & Coach Station 50th Anniversary Rally (July)

There is just a few examples, and obviously in the North East we have Seaburn/Durham and MetroCentre Bus Rallies where we can meet up also, So I would SAY there is quite a bit scope for Day Trips which could be done.