Stop on the A1

English Heritage car park at Brodsworth Hall, from junction 37 near Doncaster ?  

There are of course the Ferrybridge services, where you join the A1. Or if you don't require the actual services element, there is Clumber Park, which is only about half a mile off the A1. You do really need to be NT members though, as they have roaming wardens, who will extract a fee.

For CS then use the Wetherby services. Dedicated and wardened car park area.

Further south there is a decent stop at the Grantham services.

Not at all, it's perfectly fair. It was just a "light hearted" statement of fact to inform the OP that he could be charged if he's not an NT member. I have no idea wether the OP is familiar with Clumber. The road through is a right of way and you do not pass through any pay stations when you use it. A charge applies only when you park up on the side, or turn off it through a pay booth. I didn't want the OP surprised by a £10 / £12 bill for stopping for lunch.

Clumber with a big van on the back might not be as easy as it sounds. I can’t think of a turning circle that won’t involve going over grass,

The turning will certainly be certainly be on grass TDL, although the ultra sandy soil in this part of Nottinghamshire means this is seldom a problem unless it has been very wet for a period of time.  I'm even happy parking our 3.5 tonne MH on it.

Even midweek when we have taken the van for a run a roving warden has come along to check our card whilst we had lunch.

Finally it might be worth googling the roundabout in Kings Lynn where you turn North off the A17. It's frightening if you don't get in the correct lane and IMHO the lane markings are poor and confusing, or maybe I'm easily confused🤔

I must be easily confused as well then.😂 We did the journey a few weeks ago and it is very confusing. We had to do a bit of pushing in, as we ended up in the wrong lane.

I must admit we don't find towing through Grantham a problem but I had forgotten that it is lower down than the A17 as we tow across country and approach the A17 from the A52.  

There is a very large parking area on the A17 before you get to Sutton Bridge just past the "Bejing Palace" chinese stand alone restaurant (on the left as you drive towards Kings Lynn). There's a cafe with lorry parking area where caravans and M/hs pull over for a comfort break. This is on the right hand side of the road opposite another large establishment selling farm produce, I think. Anyway there's bags of room to pull into that car park. Only problem might be getting across the road to continue as it can get quite busy there. There are quite a few lay-bys on the A17 before Sutton Bridge just not many after.

The trick to the roundabout at KL is to use the outside of the two lanes on the slip road which then filter down to 4 lanes with the inside one to be avoided. That's the Kings Lynn turnoff. You will need the second lane as it splits into 4 which will then take you off the roundabout. There's then a small r'bout. Go straight over and uphill. You will then need the second lane at the Hospital r'bout and continue straight across and again uphill to the next r'bout where you will once again need the outside lane to turn right for the Cromer road.

Don't ask about the return. Be very aware of your lane at the big r'bout! Good luck.

That's just behind the Services at Grantham Micky and I think CS doesn't want to travel as far as Grantham but come off earlier to get onto the A17.

If he did think about Grantham then he could stay on past where the A1 goes under the A52 and come off at the next junction south. Turn left at the T junction from the slip, turn right at the lights, then after half a mile go under the railway bridge and straight across at the MacD's lights thus by passing most of the one way system that Papgeno mentions above. Once over the lights it's then a straight run along the A52 until it meets the A17.

Beginning to sound like an old Monty Python sketch.