Someone else looked at this last year, inc Biggar.
Biggar is too out of the way,imo, maybe near Gt/Inners/Drumlanrigg etc but too far geographically from the rest/West end.
Gt from Dumfries via Moffat and the Beef Tub rd is at best onl 1.5hr(1hr12min!!)
Dumfries is really your best option, lots of pubs and eateries(not city standadrs unfortunately)
What is missing from Dumfries area is cheap bothy/bunkhouse accomodation. There is no shortage of B&Bs catering for bikers, but for groups there is only Marthrown of Mabie outside of town. Mabie house is putting in more Pods. The Pines golf centre is also moving into Pods for their clientele but will be available to bikers and anyone else.
Ther is also no shortage of camping/caravans along the Solway coast, Sandyhills, Southerness, castle Point, Kippford, Glenearly and Beeswing near Mabie.
Bunkhouse and Pods is the way to go. Getting it on a bus route(what buses?) is the hardest thing tho!!
from someone in Dumfries btw who has cruised these forums for some time!!!!
Have you tried the property centre for buildings etc?
or Smiths Gore for country dwellings?