I was considering Dinard but my Jepps flitestar comes up with no customs.
Jepp Flightstar is absolutely useless when it comes to anciliary information of that sort. Check out the landing fees it quotes if you want a real laugh, but under no circumstances use Flightstar's airfield data as an alternative to proper flight planning.
So... Dinard does in fact have customs.
Does this revelation open up any additional options that you had previously closed off.
As a fellow 421 owner (recently sold), you can get to most of Europe for a weekend if the mood grabs you, the choices are limited only by your ambition.
Why don't you start of by suggesting a country or two that you really fancy visiting and maybe you'll get some focussed suggestions.
2D