Dont think Fordoun is still active but Edzell still accepts arrivals with some notice, not sure if you can park up for a few days though?
Insch is a nice strip but very tight, especially in a PA28 with low hours so you might want to rethink that one. Local C172 pilots generally require a checkout before being allowed to operate from Insch due to surrounding terrain etc, its also closed a lot of the time if we've had a run of wet weather.
To be honest, by the time you muck about getting from Insch / Hatton your as quick landing at Dundee and getting the train up from there. Landing fees are pretty reasonable, the people are friendly and it has good facilities, IE Fuel which you wont get at Insch or Edzell!