Hello GMJ. We stayed near Frankfurt in a delightful small town just on the north-east side, called Gelnhausen. The town itself is very pretty with hills behind and plenty of walks through the forest. Down in the valley, there is a magnificent lido. There is a train station so easy access into Frankfurt. At the time we did not own a van so I cannot recommend a campsite, but I would guess there is bound to be one near the town. Good luck!