About 210Km from Calais (takes about 5hrs towing) is a site called Camping St Nicolas at Le Bec-Hellouin. Can highly recommend it. Has good clean facilities, I believe it now has a pool and a small bistro/bar, and there is (was free) wi-fi. Nearby Brionne has a decent sized Carrefour for shopping. There is only one piece of payage autoroute near Boulogne which is easily avoided by using the D901 and D940. You will see much more of France if you keep off the autoroutes.
If going to France as a couple do you want a seaside break or have interest in exploring France? Agreed Brittany and the Vendee are both worth visiting (or going a bit further south to Cognac) but the Loire as a first time visit takes some beating. Angers and Saumer on the Lower Loire are good places to go, and if you like light white wines then Sancerre on the Upper Loire is a good base. The municipal Camping Paulin-Roulin at Crezancy-en-Sancerre is small, superbly kept, and very quiet but no pool or anything like that. Only has eight pitches all with 10A electrickery! Call before visiting as there is a height barrier on the entrance and you will need to speak a bit of French. From Le Bec you go to Evreux, Dreux, Chartres, Orleans, Vierzon, and Bourges all of which have by-passes or ring roads. Bourges is a nice place to have a wander around and also has a good municipal, and just up the road is Mehun where they make Pillivuyt porcelain and have a factory shop that sells (essentially perfect) seconds by weight! (Ask SWMBO.)
In terms of caravanning in France:
Most supermarket/hypermarket fuel station pumps accept UK credit cards and often speak to you (oh yes, talking petrol pumps!) in English as well. If you have time and do not have one get yourself a Visa card (M/C is not so widely accepted in France) that does not charge for transactions - Nationwide, Santander, and I think Halifax do them. The advantage of using a CC is that it gets transferred from Euros to sterling at bulk rate which you won't beat anywhere in the UK. If you buy anywhere and pay by credit or debit card ALWAYS pay in Euros as the rate will be better (but as an experienced traveller you probably already know that.)
Be aware that most French sites limit power to 6A so unless you want to use up your gas get yourself a lower power kettle - 1KW for example. Some sites limit to lower (I have seem 3A) when you will have no option but to use gas, but others are getting better and allow 10A or even 16A!
Some sites use the blue EHU connector that we use but many still use the standard continental Schuko connector so you will need an adapter. Either make one yourself or get one from such as Towsure - it needs to be a right-angled Schuko plug with the socket for the earth pin at the top opposite the cable direction or you may not get it into the connection box on site.
In France, due to a protruding earthing pin, you will not be able to reverse the Schuko plug in the socket if the polarity is incorrect.This will start a row on here but unlike the UK where we use single pole (i.e. live wire) switching the Schuko system uses double pole breakers or switches so if it trips it takes out both wires, live and neutral. As a consequence the French (most of EU in fact) don't both about supply polarity when wiring up socket outlets. For safety it is a good idea to get a short length (about 1m) of 2.5mm orange flex and a blue plug and socket. Wire one end correctly (L&N) as marked on the connector but reverse the L&N wires at the other end. You will also need a 13A plug-in polarity tester to confirm correct connection (Towsure again.) The green/yellow earth wire is connected direct at both ends - whether there is an earth actually connected to the supply is a different matter altogether!
Finally, if you have the spare payload capacity on your van it is worth taking a second EHU cable as the run on some sites can be long.........
And finally finally, WATCH YOUR SPEED. The French have just reduced the speed limit on non-autoroutes to 80Kph (was 90.) They use a lot of fixed and mobile speed cameras and indeed now have an outside company doing radar speed checks from moving vehicles (differential measurement I believe.) If you get flashed expect to find a speeding ticket waiting when you get home. You can of course ignore it but you may find it a tad difficult to get into France next time! Cars coming towards you flashing their headlights usually means a speed trap ahead - and it is not uncommon to find two in series perhaps 1Km or so apart - you get caught by one, breathe a sigh of relief as you leave the scene, and get caught again! If the Gendarmes are out stopping speeders it can sometimes be several Km down the road after the radar location.
I hope this does not frighten you but getting all these bit and putting them is a fact of life which you need to establish before your first trip - but you only have to do it once!
Have a good trip.
PS
Get a Michelin France road atlas - it is by far the best for France.