Country airports are there for use by all aviators and their passengers not just RPT ops.
And the airport
is available to all, however some buildings and infrastructure may not be, at the discretion of the Airport Operator. It's the wonderful world of user pays, and you are not the user. Perhaps a call ahead to check the status of the facilities and maybe ask how much would it cost for the facility to be made available for the use of you and your passengers during your stop?
I know when I was involved with a regional airport, the Terminal facilities was locked up between RPT flights, but we did provide a pretty good ablution block for the use of itinerants, however, this was constantly getting trashed and costing a fortune in maintenance, so we removed it.