Wigan Warrior,
You can't go too far wrong in France, but here are some thoughts.
If you don't mind a slightly longer sea crossing then you can go straight from the Isle of Wight to Cherbourg and clear customs there. That will be a reasonably direct route for you. I went that way last Friday on my way to a very pleasant day in/on Belle Ile, just south of the Brest peninsula. Other nice spots in that area are La Baule and, a little further down the coast, La Rochelle.
On Saturday I flew back up to Bernay which is a very charming grass field with an excellent small hotel and restaurant on site.
From there it was a short hop up to Deauville which is somewhere else you could consider, though I don't think I'd want (or be allowed to) camp on the airfield. It is a customs field though. A taxi into Trouville is about 17 euro, whereas one to Honfleur (a similar distance) is about 35. Pourqoui? Je ne sais pas, or 'search me guv' as they say in the taxi trade.
Both are nice spots, though the whole coast was booked out last weekend and I ended up in an Ibis near the oil refineries of Le Havre
I think there was something on in the area though, so that isn't usual.
On the western side of the Cherbourg peninsula is Dinard, which will do customs for you and is handy to St Malo. I flew into the airfield in March, but didn't go into the town. I'm sure St Malo offers plenty of good dining and shopping opportunities though.
Moving further up the coast, but avoiding Le Touquet, you have Abbeville. You can camp there, though there's a motel on site. There is also a good restaurant on the field, and the town is quite close too.
Skipping L2K, you get to Calais. I've been there several times this summer but it must be said the facilities at the field are a little limited. You need prior notice for customs, but again, it's not exactly an idyllic camping spot. I suppose the shopping is good if you want to stock up on booze, though you'd need a taxi or rental car.
Personally I'd probably cross from the IoW to Cherbourg and keep going to either Dinard or Deauville. If you have more time, or a particularly swift PA28 (relatively speaking of course) then try for La Baule or La Rochelle.