GPs are normally run in 18m class.
My Australian club, Lake Keepit www.keepitsoaring.com has hosted a couple of Qualifying GPs. The last one (November 2014) was run in 15m class. They have a couple of gliders to rent that would be fine in a 15m QGP: Discus 2B and 2C. Also an LS7 if those aren't available.
Keepit has hosted a GP training camp (Bruce Taylor is a club member and loves the GP format), and even ran a GP for Open class/2 seaters.
There are cabins and clubhouse bedrooms available on the airport, and other cabins available a mile or so away in the Lake Keepit State Park.
This is probably not a one-of-a-kind. Other Worldwide GP locations may offer similar resources, so have a look.
Jim