Whatever airfield you choose, it takes at least a one hour drive from city centre to get there. Stendal airfield offers nice and plenty of hangarspace for classic gliders, but it's a rather small gliding community over there (nice people, though). Reinsdorf is probably the best airfield to get away from (great thermals), but has only very limited hangar space. Neuruppin may also be worth a visit, there are also some pieces of wood flying around.

Cheers,
Christoph