For a 6-hour journey, there are plenty of places that could work well. I'd suggest looking for service stations or rest stops with grassy areas, especially those that have designated dog-friendly spaces. Many places have toilets and a bit of green space, so Pinto can stretch his legs. You could also check for caravan-friendly stops along the way for a smoother journey.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.