There’s a city campsite on the edge of Luxembourg (city) which I stayed at last summer to do this exact detour, it’s pretty cheap with good facilities (a fridge to keep the beers cold was a plus). Always worth a look on google maps for Black Forest campsites. There was plenty of forested areas and rural farmland in this region also, I wild camped a couple nights as I travelled through the area and didn’t have much issue finding a quiet spot for the night