Landing a PA28 at Baisy-Thy is illegal - and might land you in some fun with the a/d operators, on top. And again, I really can't imagine a PA28 can be safely operated on a 300-odd meters runway; but then, I am only a newbie microlight pilot.
There's not many alternatives: there are several other ultralight terrains about, EBBZ, EBLN, EBAV are not too far, but just like EBBY they have neither the required runway length nor the authorisation for a PA28.
Your best options might be Grimbergen EBGB, just to the North-West of Brussels, or EBNM Namur. Both are very nice club aerodromes. Namur is busy with gliders and paradrop, and do most of their radio in French. Grimbergen OTOH is plagued by nimby's worse than any other a/d, so their procedures are VERY strict and you really MUST respect them.
Also see my remarks about clearing customs - I think our messages crossed each other. You will have to pass by a more or less expensive a/d anyway!
As for radar coverage: controlled airspace is closed to me, so I can only speak for Brussels Information @ 126.900 MHZ, who are in charge of uncontrolled Belgian airspace. This is a great crew, who will cheerfully inform you of other traffic at your altitude, activate flight plans or even file them if you pretend to have forgotten, get you cleared for going higher up &C. The frequency tends to get busy on sunny weekends, though.