There's also Chester services on M56. The Shell/OK diner one at Northop has poor parking for caravans and you may struggle. I think quite a few new layby's have gone in over the last year or so, they may be a better option if just a quick break.
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.